Chapter 6: Growing Underground Crops: Carrots, Onions, and Potatoes

In This Chapter

Choosing the best carrot, onion, and potato varieties for your garden

Growing, caring for, and harvesting your roots

Controlling root pests and diseases

Root-crop vegetables are an example of those good things in life that you can't actually see. Their tops are green, unassuming, and may even be mistaken for weeds — but oh, when you give them a yank! I can still remember the look on my daughter's face when she first helped me dig potatoes and discovered that they grow underground. Digging for potatoes was like a treasure hunt. I think that most gardeners feel that same sense of wonder and excitement when they dig or pull up their root crops. The result is always something marvelous.

You can grow many different root crops, but the big three are carrots, onions, and potatoes. They aren't botanically related like peppers, eggplants, and tomatoes are (see Chapters 4 and 5); what these crops do have in common, however, is that they're grown for their underground parts: roots, bulbs, or modified stems (underground stems that expand to produce large, edible areas; potatoes' stems are called tubers). I provide plenty of growing tips for carrots, onions, and potatoes in this chapter; I discuss other root crops in Chapter 11.

A Rabbit's (and Gardener's) Favorite Root: Carrots

Carrot (Daucus carota) varieties are categorized by their shape. You can grow long, thin carrots; short, stocky carrots; and even little, round, baby carrots. A few varieties are supercharged with vitamins, and many hybrids have added vigor and disease resistance. The latest trend in carrots is colorful roots. Roots no longer come in just orange — now you can grow varieties that are white, yellow, red, and purple, too!

If you're trying to decide which carrot variety to grow, consider your type of soil as well as the use you plan for the carrots. Loose, sandy soil is good for growing any root crop. If you have heavy, clay soil, consider a variety that's shorter in length, such as ‘Short 'n Sweet'. It's easier for this short carrot variety to push into the heavy soil than a long, thin, tapered root variety. (Chapter 14 has more information about soil types.)

Classifying carrots by type

Carrots often are described as a certain type, such as baby carrots. If the carrot type is part of a variety name, you can determine what the carrot will look like when it matures. Table 6-1 shows the common types of carrots and their characteristics. All the types listed, except baby carrots and Imperators, range in size from 6 to 8 inches. Aside from eating the carrots fresh, you can best use certain varieties for juicing and storing; some even grow well in containers.

Most short varieties that you find in grocery stores are baby carrots, and the longer carrots may be any of the other types mentioned in Table 6-1. The bagged "baby-size" carrots in grocery stores are often just normal-sized

carrots peeled down to a small, rounded size. Look for carrots with the tops still showing for true baby carrots. Baby carrots may be varieties that are naturally short or larger varieties harvested at an immature stage.

Examining some carrot varieties

Knowing what type of carrot a certain variety is can help you when deciding which variety to grow. With some of the most widely known carrot varieties, you can easily identify the carrot type because it's part of the variety's name; some examples include ‘Scarlet Nantes' and ‘Danvers 126'. Otherwise, you simply read the description to find out.

The carrot varieties in the following list fall into one of the five types of carrots identified in Table 6-1, but they also have special characteristics that may make them perfect for your garden; they're flavorful, disease resistant, and easy to grow. All are good for baking. The days to maturity are from seeding in the ground until first harvest; however, early season carrot varieties are flavorful even when you harvest them before they fully mature:

‘Atomic Red': This Imperator-type, open-pollinated carrot features 9-inch-long roots that are red from skin to core. The color deepens and flavor becomes milder when cooked. This variety matures in 70 days.

‘Bolero': This hybrid, Nantes-type carrot produces 6-inch-long roots and 8135*has extra disease resistance and stores well. It matures in 72 days. ‘Yaya' is a newer hybrid Dutch variety that's sweeter and matures earlier (60 days) than ‘Bolero'.

‘Danvers 126': These heat-resistant, open-pollinated roots produce heavy yields of 7- to 8-inch-long carrots 70 days after planting.

‘Healthmaster': This hybrid, Danvers-type variety grows up to 10 inches long and contains 30 percent more vitamin A than other carrot varieties. It matures in 110 days.

‘Kuroda': This hybrid, 6-inch-long, Chantenay-type produces heavy yields of tender carrots that are good for juicing and storing. It matures in 79 days.

‘Little Finger': This open-pollinated variety is an early (65 days), 3-inch-long, smooth-skinned, small-cored baby carrot that's sweet. ‘Little Finger' carrots are great for planting in containers.

‘Merida': This hybrid, Nantes-type, 7- to 8-inch-long carrot can be planted in spring for fall harvest. However, it's most often grown as a fall crop and in mild-winter areas, such as the Pacific Northwest, where it can overwinter (live through the winter) and be harvested in spring. It matures in 75 days.

‘Parmex': This hybrid, baby-type carrot features 1 1/2-inch-diameter round roots that are harvested in 50 days. Great for planting in shallow soils.

‘Purple Haze': This hybrid, 10- to 12-inch-long Imperator has purple skin and an orange core. This sweet variety's purple color fades when cooked. It matures in 70 days.

‘Scarlet Nantes': This heirloom, Nantes-type variety has bright red-orange flesh with a small core. The 6- to 7-inch-long roots mature in 65 days.

‘Short 'n Sweet': This 4-inch, open-pollinated, Chantenay-type carrot grows well in heavy clay soil and containers. It matures in 68 days.

‘Sugarsnax': This hybrid, Imperator-type variety is as tender and sweet as a Nantes variety, yet it grows up to 9 inches long, is disease resistant, and is high in beta carotene. It matures in 68 days.

‘Thumbelina': This unusual hybrid, baby-type, All-America Selections winner (see Chapter 4) has a round root that's the length of a silver dollar; it's especially good for baking. It grows well in containers and in heavy clay or rocky soil. It matures in 65 days. Kids love this variety for its small size and easy-growing nature.

‘White Satin': This hybrid, Nantes and Imperator cross features 8-inch-long crisp, textured white roots that grow under a wide range of soil and weather conditions. It matures in 68 days.

Onions: The Bulbs with Layers of Sweet and Pungent Goodness

The two most important factors to consider when choosing onion (Allium cepa) varieties are flavor of the onion and location of your garden. Although most people use taste as their first criterion, the old advice about "location, location, location" has greater relevance when growing onions. Onions are particular about how much sunlight they get, forming bulbs in response to the number of daylight hours. As a result, onion varieties are classified by day length — long day, short day, or intermediate day (also known as day neutral) — as well as by taste — sweet (which are good for eating raw or freshly cooked) or pungent (which are good for storing).

In general, short-day onions grow well in the southern United States, long-day onions grow well in the northern United States, and intermediate-day onions grow well in the in-between regions.

See the later sidebar "What a difference a day makes!" if you really want to get into a discussion on day length and onions. If you want to avoid the whole issue, try growing some fun onion relatives, such as leeks, garlic, and shallots, which I discuss in Chapter 11.

Choosing your onion varieties

In the following lists of my favorite onion varieties, I distinguish between onions that are long day, short day, and intermediate day (or day neutral). Within each group are sweet and pungent varieties. These varieties are the most widely adapted (able to grow in a wide variety of geographic regions under various weather conditions) and easiest to grow. Keep in mind that pungent onions are much better for storage than sweet varieties. (You can read more about storage in Chapter 19.)

I also indicate whether you can purchase the variety as a set (small onions that have been pregrown so that they mature faster) or as a plant (or both). (Check out the appendix for a listing of companies that specialize in onion sets and plants.) The days to maturity are from either directly seeding in the garden or setting out (placing outdoors) sets or plants. Short-day onions are generally planted in fall to grow through the winter, so they take longer to mature than other types. Long- and intermediate-day onions are usually planted in spring. All the onions have yellow skin and white flesh unless otherwise noted.

Short-day onions include the following varieties:

‘Giant Red Hamburger': This open-pollinated, sweet, short-day variety features dark red skin and red-and-white flesh. It matures in 95 days from seeding and can be purchased as a plant.

‘Granex 33' (Vidalia): This classic hybrid sweet onion is a well-known short-day variety. It is available as a plant and is popular in the Southeast. It matures in spring, 180 days after fall seeding.

‘Texas Grano 1015' (Texas Supersweet): This sweet, short-day, hybrid variety can grow as large as a baseball and still remain sweet. It's also available as a plant and is popular in Texas and in the Southwest. It matures 175 days from fall seeding.

Intermediate-day (or day-neutral) onion varieties include the following:

‘Candy': This sweet, hybrid, intermediate-day onion is widely adapted. It's also available as a plant. It matures 85 days after seeding.

‘Italian Red Torpedo': This sweet, Italian heirloom, intermediate-day, red onion forms a bottle-shaped bulb with a mild taste and pink flesh. It matures 110 days after seeding.

‘Superstar': This All-America Selections winning, hybrid, white-skinned, sweet onion produces a 1-pound, disease-resistant, uniform, mild-tasting bulb 109 days from planting. It's isn't good for long-term storage because of its extra sweetness.

Long-day onion varieties include the following:

‘Ailsa Craig Exhibition': This yellow-skinned, open-pollinated variety is known for its sweet, 2-pound bulbs that mature 105 days after seeding. It tolerates cool weather well.

‘Borrettana cipollini': Cipollini are unique heirloom, Italian, flat-shaped varieties. The ‘Borrettana' variety produces 2-inch-diameter yellow sweet onions that are great braided and good caramelized and sautéed. It matures 110 days after seeding. ‘Red Marble' is a good red cipollini-type variety.

‘Copra': You can store this hybrid, pungent variety until spring. It matures 104 days after seeding.

‘Purplette': This open-pollinated, purple-skinned mini-onion is best harvested when 3 to 4 inches in diameter 60 days after seeding. It has mild, sweet pink flesh and is a good one for pickling. It also can be used as a scallion (see the next section).

‘Yellow Sweet Sandwich': This hybrid variety actually gets sweeter in storage and comes in a white-skinned version called ‘White Sweet Sandwich'. Both versions are available as plants. The variety matures 100 days after seeding.

‘Walla Walla Sweet': This sweet, hybrid variety has light yellow flesh and good cold tolerance. It's available as a plant and is popular in the Northwest. It matures 115 days after seeding.

‘Yellow Stuttgarter': This pungent, standard, open-pollinated storage variety often is sold as a set. It matures in about 90 days from a set and 120 days after seeding.

Looking at scallions and perennial onions

You may have run across some other onion types in restaurants or produce markets. For example, scallions (also called bunching onions, spring onions, or green onions) are picked for their delicate, juicy, green tops before they form bulbs. Scallions take up less space in your garden than regular onions because you can plant them closer together, and they can give you a quick crop when planted in spring or fall. Growing scallions is a good way for novice onion growers to start.

Any onion variety grown from a seed can be harvested as a scallion, but here a few varieties that are especially widely adapted as scallions:

‘Evergreen Hardy White' (Allium fistulosum): This hardy, white-stalked variety is a great one for cold climates (USDA zone 5), and it can overwinter if protected and used as a perennial. It matures 65 days after seeding.

‘Red Beard' (Allium fistulosum): This tender variety has unique coloring: a red stem with a white tip and green leaves. It matures 45 days after seeding.

‘White Spear': This heat-resistant scallion features blue-green leaves and thick white stems. Good for warm climates. It matures 65 days after seeding.

Multiplier, or perennial, onions come back year after year and reproduce easily. Here are the two main types:

Egyptian top-set onions (also known as walking or tree onions): These onions reproduce by forming clusters of onion sets on the tips of their growing stalks, as shown in Figure 6-1. As the weight pulls the stalks down, the clusters root wherever they land, making the onions look like they're walking slowly across your garden. During the winter months, Egyptian top-set onions primarily are eaten as scallions, but the top-sets make good, small, sweet onions when you pick them in summer. They're also very cold hardy.

Potato onions: These onions form a main onion in summer from a fall planting. They're hardy to USDA zone 4 and produce many smaller sets that you can replant after summer harvest to produce more onions the following year.

Potatoes: No Longer a Boring Spud

If I had to vote on the most underrated vegetable in the world, I would choose the potato (Solanum tuberosum). Potatoes have a reputation for being common, widely available, inexpensive, and just plain brown and boring. Why bother growing them? Well, first of all, the flavor and texture of fresh potatoes dug from the soil is much better than the bagged spuds that sit on grocery-store shelves for weeks. It's also fun to grow the many different varieties, including novelty potatoes such as purple-, red-, or yellow-fleshed varieties. You'll surely astound your family and dinner guests with these not-so-plain potatoes.

Potatoes are one of the most foolproof crops to grow. Start planting early, while the weather is still cool, by placing a piece of the tuber (called a seed potato) in a furrow, or trench. After the potatoes start growing, if you hill them (push soil around the plants), water them, and keep the bugs away, you're almost guaranteed some great tubers. I explain more about planting potatoes and provide tips on growing sweet potatoes, a special kind of root crop, later in this chapter.

Potatoes classified

Potato varieties usually are classified as early-, mid-, and late-season from the time you plant the seed potato to harvest. If you have a short growing season, grow early-season plants. If you have a longer growing season, you'll be safe with the late-season plants. If you want to have a constant supply of potatoes all summer, grow a few of each. Table 6-2 shows the approximate number of days to maturity for each category.

Selecting a few potato varieties

So many potato varieties are available that narrowing the field is often difficult. However, you may want to try some of my favorites, which I describe in the following list. I've included some fingerling varieties that are the latest rage; they produce an abundance of small, fingerlike tubers that are great roasted, fried, or steamed. Here are my favorite potato varieties in terms of flavor, color, and ease of growing:

‘All Blue': This mid- to late-season spud has blue skin and flesh. It has a mealy texture, so it's best as a mashed potato. Yes, blue mashed potatoes! You also can grow a similar ‘All Red' (also known as ‘Cranberry Red') variety that has red skin on the outside and pink flesh on the inside. Combined with ‘All Blue' potatoes and a white variety, you can create a red, white, and blue mashed potato extravaganza!

‘Butte': This late-season variety is the classic Idaho baking potato. It's a great russetted (has rough, brown-colored skin) baking variety that features 20 percent more protein and 58 percent more vitamin C than other varieties. It's also tolerant of scab disease and late blight. (See the later section "Keeping Your Root Crops Healthy and Pest-Free" for more on these problems.)

‘Caribe': This early, lavender-skinned, white-fleshed variety produces large tubers. A great masher.

‘Kennebec': This all-purpose midseason variety with white skin and flesh is dependable, resists disease, and is good for almost any use.

‘King Harry': This early-season, gold-skinned and white-fleshed variety is unique for its hairy leaves that reportedly ward off insects, such as Colorado potato beetles, leafhoppers, and flea beetles (see Chapter 17). Oh, and the spuds taste great, too!

‘Red Norland': This early variety has red skin and white flesh. Harvested early when plants are just flowering, this variety is commonly sold in markets as a new red potato. It tastes best boiled or mashed.

‘Rose Finn Apple': This late-maturing fingerling variety features rose-colored skin and yellow flesh. It has a firm, moist texture and is great baked or boiled.

‘Russian Banana': This late-season, fingerling-type variety has a banana shape with a waxy yellow skin and flesh. You'll find it great for roasting and boiling.

‘Superior': This early-season tuber has buff-colored skin and white flesh. It's scab disease-resistant, grows under a wide range of conditions, and stores for a long time. A keeper!

‘Viking Purple': This midseason, purple-skinned, white-fleshed variety can endure dry weather and stores well. It tastes great boiled or mashed.

‘Yukon Gold': This very early variety with yellow skin and flesh produces high yields and is drought tolerant. It's a great keeper; in fact, I've been known to still be eating this variety from storage 8 months after harvest. This moist-fleshed potato is best in salads or boiled. Plus it makes a great chip!

Even though most potatoes are grown from seed potatoes, you can grow potatoes from seeds just as you do with tomatoes and peppers. One hybrid, late-maturity, true-seed variety that's currently available is called ‘Catalina' (which is very similar to ‘Kennebec'). For best results, start seeds indoors a month before planting. You grow your crop the same way that you grow other potatoes. Growing potatoes from seeds is a bit trickier but less expensive than planting seed potatoes, and you reduce the chance of passing on any tuber-borne diseases to your new crop. (See the later section "Keeping Your Root Crops Healthy and Pest-Free" for more on potato diseases.)

Growing and Gathering Root Crops

Root crops are easy to grow if you have good soil, water, and proper spacing. The mystery of root crops is that you can't see the reward until you dig them up. But that's half the fun of growing them.

General guidelines for all your root crops

The keys to growing great root crops are preparing the soil bed well and giving the plants room to grow. You also need to keep the crops clear of weeds and make sure they have enough water. Here are further details on each of these important points:

All root crops like well-drained, loose, fertile soil. And with the exception of potatoes, which grow best in hills (as you find out later in this chapter), root crops grow best in raised beds (see Chapter 3 for more on these special beds). They also can grow if you have a gardening spot that gets only 4 to 6 hours of direct sun a day. Try some carrots and onions in that patch.

To prepare the soil, add a 3- to 4-inch layer of compost or manure at least 2 to 3 months before you're ready to plant. If you wait until just before planting to add fresh compost or manure, you're likely to get poor growth. Why? Too much nitrogen fertilizer on carrots and potatoes in spring promotes foliage growth but not good tuber and root formation. Instead, root crops enjoy phosphorous, which promotes root growth, so perform a soil test (see Chapter 14), and based on the results, add bone meal or rock phosphate fertilizer before planting to keep your roots happy.

Onions in particular like lots of fertilizer, and they can stand some extra nitrogen, which promotes leaf growth. Add extra fertilizer when the transplants are 6 inches tall and the bulbs begin to swell. Then add a complete organic fertilizer, such as 5-5-5, at 1 pound per 10 feet. (See Chapter 15 for more on fertilizers.)

Root crops, especially carrots and onions, require proper spacing to grow at their best. Thin out the young seedlings when they're 3 to 4 weeks old by pulling them out or snipping them until they're properly spaced (see Chapter 13 for details on thinning seedlings). Onions should be 4 inches apart, scallions 2 inches apart, and carrots 3 inches apart. Potatoes don't need thinning and should be planted 8 to 10 inches apart when planted.

I know that thinning your hearty crops sounds cruel, but if you don't do it, the roots won't have enough room to expand, causing you to get lots of plants but few roots — and fewer roots means fewer carrots and onions.

You'll be rewarded with lots of crisp roots in no time if you regularly weed your root crop patch. After a good thinning, hand-weed beds of carrots and onions; potatoes can be weeded with a hoe. Mulch the bed with hay or straw. You don't have to mulch in between individual onion and carrot plants. Simply mulch around the beds, and keep them well watered.

Carrots, onions, and potatoes are root crops that like cool temperatures. They grow best and have the best flavor when temperatures stay below 80 degrees Fahrenheit.

Cultivating carrots

Carrot seeds are small and take up to 2 weeks to germinate, so you run a greater risk of poor germination with them than with other vegetables. To get your carrots off on the right foot, try these tips:

Prevent forked roots in carrots by making sure the soil is free of rocks, sticks, and hard pieces of soil. If carrot roots come in contact with a hard object as they're growing, they fork, creating a multipronged carrot. Even though they're interesting to look at and a conversation piece at dinner, forked roots are harder to clean and yield fewer carrots. No soil can be completely free of rocks and sticks, but when building a raised bed try to remove as many as possible. And be sure to amend the soil with compost to make the soil looser so the roots stay straight. If your soil is heavy clay or a rock jungle, try growing round varieties such as ‘Thumbelina'.

For easier germination of small carrot seeds, try purchasing pelleted seeds. These seeds are covered with a biodegradable coating, making the seed larger and easier to handle. However, the seed germination isn't affected. Sprinkle carrot seeds on the top of the soil and then cover them with a thin layer of potting soil or sand. Potting soil and sand are lighter than garden soil, enabling tender seedlings to more easily grow through.

Keep your soil moist. If it dries, the seedlings can quickly die. (See Chapter 15 for more on watering.)

Grow carrots as a fall crop, starting 1 to 2 months before your first frost date. They germinate faster in the warmer soil of summer, and their flavor is sweeter when they mature in cooler fall weather. In hot-summer areas, you may need to shade your newly sown soil with a shade cloth; hot soil temperatures hinder proper seed germination. (The appendix has more on frost dates.)

If your carrot tops break off during harvest (some always do), use a garden fork to dig up their roots. Pull the largest carrot roots first to leave room for the smaller roots to fill out. And if you can't eat all your carrots before the first freeze, lay a 6- to 8- inch-thick layer of hay or straw over the carrot bed. This layer of protection will keep the soil thawed, allowing you to go out on a winter's day and harvest fresh carrots right until spring.

If you're really hungry for carrots and can't wait until they fully mature, you can harvest young carrots anytime after the roots have formed. They just won't taste as sweet unless you grow the baby types.

Growing onions

The simplest way to grow onions is from a set or plant. But you can also directly sow onion seeds in spring, 2 weeks before your last frost date, or start them indoors 8 weeks earlier. For a fall planting of onions, start seedlings indoors or buy transplants. Plant the onion plants 4 to 6 weeks before the first frost. If you're starting your own seeds for a fall planting, start them indoors 8 weeks earlier.

If you start onions indoors, keep the plants stocky and short; whenever they get long and straggly, cut the tops with scissors so the plants are 3 inches tall. Trimming encourages better root growth and keeps the plants at a manageable size. Keep the seedlings moist and grow them under lights (Chapter 13 has more on growing seedlings indoors). Then harden off the transplants — gradually introduce them to the outdoor growing environment by bringing them outside for longer amounts of time each day for up to 1 week; then plant them 4 to 6 inches apart.

What makes onions pungent or sweet? The sulfur, not the sugar. Sweet onions have less sulfur than pungent varieties, so they taste sweeter. Even though the sulfur can make the onion more pungent, it also makes those varieties great storage onions. To keep your sweet onions as sweet as they can be, don't apply any sulfur fertilizers. Also keep the onion plants stress free by controlling weeds and making sure that the plants receive enough water and fertilizer (such as 5-5-5). If you do so, they will thrive and be sweet.

You can harvest onions anytime if you want scallions or small, baby onions, but for the largest bulbs, wait until about 80 percent of the tops have naturally started to fall over. Pull the bulbs out on a dry day if possible and then let them dry out in a warm, shady spot. For more on harvesting, see Chapter 19.

Producing potatoes

Potatoes are mostly grown from seed potatoes, which are either small potatoes or larger ones cut so that each piece has two eyes (those small indentations on a potato's skin). Eyes are dormant buds from which roots and shoots grow. Plant pieces about 8 to 10 inches apart in rows.

Don't try to plant potatoes that you purchase from a grocery store. These spuds have been treated with a chemical sprouting inhibitor, so they either won't grow any plants or the plants will be weak and not productive. It's best to purchase seed potatoes from a mail-order catalog, nursery, or garden center.

In this section, I describe essential techniques for growing potatoes.

Protecting your taters with the hilling technique

If you weed your root crop patch, mulch it with hay or straw, and water it well, crisp roots will be yours for the taking in no time. However, potatoes do require one more special technique, called hilling. Hilling is the technique of mounding up the soil with a hoe around the plants as they grow (see Figure 6-2). Hill at least twice during the growing season — about 1 week after the leaves emerge from the soil and again 2 to 3 weeks later. Hilling promotes the production of bigger potatoes and more of them, kills weeds, and keeps the sun off the tubers.

After your final hilling, lay a 3- to 4-inch-thick layer of hay or straw around your potatoes. Not only will this layer reduce the amount of weeding you do the rest of the summer, but it also will keep the soil cool and moist — perfect tuber-forming conditions! This layer also helps create larger tubers with fewer problems, such as hollow heart (when the center of the potato is hollow due to moisture stress).

Any direct sun on potatoes causes chlorophyll to form, turning the potato skins green and giving them an off taste. Tubers actually are mildly poisonous after they've formed chlorophyll, but you'd have to eat a truckload to really get sick. Keep the potatoes hilled and mulched when in the ground, and store them in the dark after harvest to avoid this problem. If you have a small green patch on your potato, just cut if off; the rest of the tuber is fine to eat.

Applying a space-saving planting technique

Don't have room in your garden but want to grow potatoes? Instead of planting in rows, try growing potatoes vertically in potato towers (see Figure 6-3). Here's how:

1. Place a 3-foot-diameter heavy wire cage over cultivated soil.

2. Add a 2- to 3-inch layer of soil to the bottom of the cage, and line the sides of the cage with hay. Plant four seed potatoes in the bottom of the cage and cover them with soil.

3. As the potato plants grow, continue adding soil over them and adding hay around the inside of the cage until you reach the top of the tower. Keep the soil well watered.

4. In the fall, open the cage and watch your tubers roll out!

Digging up the fruits (er, vegetables) of your labor

Harvesting potatoes is like going on an archeological dig. After a potato plant dies, use a metal garden fork and dig up the area 1 foot away from the row so you don't spear the tubers. You'll be amazed at the number of tubers you find — on average, 10 to 20 per plant. Dry the potatoes for an hour or so in the shade, and then store them in a dark, airy, 60-degree area for curing (the process of letting the skin toughen so the vegetables store better). After 2 weeks, move the potatoes to a shed or room that's 40 to 50 degrees to store for up to 9 months (depending on the variety). Always eat any damaged tubers first, because they'll be the first to rot in storage.

New potatoes are just young potatoes, and with their soft skin and texture, they make a great summer treat. If you can't wait until the main harvest is ready, steal a few new potatoes the second time you hill. Just reach into the soil and feel for small, round tubers. Taking a few won't kill the plant, and you'll still get some larger spuds later on.

The sweetest of tubers: Planting sweet potatoes

Sweet potatoes (Ipomoea batatas) are a root crop with a reputation for being grown only in the South. However, if you choose the right varieties, you can grow sweet potatoes just about anywhere — even in cold climates like Minnesota. Sweet potatoes are easy to grow and store well indoors in winter. The orange- or yellow-fleshed tubers can be baked, mashed, or sliced and deep fried for a nutritious and delicious snack. Some short-season varieties (90 days) to grow are ‘Beauregard', ‘Centennial', and ‘Georgia Jet'. Other varieties that mature 1 to 2 weeks later are ‘Bush Porto Rico', Jewel', and ‘Vardaman'.

To grow sweet potatoes, you don't plant seeds. Instead, you buy small plants called slips. Slips are available at local nurseries or garden centers in spring or through the mail. You can start your own at home, but it's better to purchase certified disease-free slips from commercial growers to avoid disease. Sweet potatoes love the heat, so wait until the soil temperature is at least 60 degrees before planting. The vines of your sweet potatoes will create a dense, mat-like groundcover, making this an attractive and edible plant to grow.

To plant and grow your sweet tubers follow these steps:

1. Create raised beds at least 6 inches tall and amend the soil with compost.

2. Plant the slips up to their bottom leaves, 1 foot apart in the raised beds.

In cold-winter areas, consider laying black plastic over the beds, punching holes, and planting the slips through the plastic so the soil will heat up faster and the tubers will grow and mature sooner.

3. Side-dress the plants once, a month after planting.

When side-dressing, use an organic fertilizer, such as 5-5-5, or a mix of blood and bone meal fertilizer. And be sure to keep your plants well weeded and watered. Keep the soil on the slightly acidic pH side to avoid some diseases. (Check out Chapter 15 for details on side-dressing and fertilizing.)

4. Before the first frost, or about 100 days after planting, dig under the plants and check for roots.

Pull plants that have formed good-sized roots and cure (dry) these in a warm (80-degree) room for 2 weeks. The curing process not only helps the skin toughen, but also converts starches to sugars, giving sweet potatoes their characteristic taste.

After curing, eat the tubers or store them in a humid, 55-degree basement (or in any other cool area of your house) all winter.

Keeping Your Root Crops Healthy and Pest-Free

Many of the same pests and diseases that you find on other vegetable crops — such as aphids, flea beetles, thrips, mosaic virus, and nematodes — also occur on root crops. Other potentially damaging root crop pests are animals — such as rabbits, mice, and chipmunks — that enjoy the underground snacks out of sight of predators. I lost most of my potato crop one year due to an overpopulation of hungry chipmunks looking for food. (I discuss insect and animal pests as well as common diseases in more detail in Chapter 17.)

Check with your local Cooperative Extension Service office or the folks at your local nursery or garden store to find out what specific diseases and insects may be problems in your area. Then, as with any vegetable, you can plant varieties that are resistant to those diseases and insects.

Besides the usual suspects that attack vegetable gardens, a few pests and diseases specifically harm root crops. Here are descriptions of them as well as the appropriate controls:

Blight: This fungal disease can wreak havoc on potatoes. Late blight, in particular, is the infamous disease that destroyed potatoes in Ireland in the 1840s, causing the Irish potato famine. This disease thrives in cool, humid weather, and infection starts in the form of water-soaked black spots on the leaves.

Unfortunately, once blight starts, you can't treat it; the plants can die, and any tuber that they produce also may be infected and inedible. To avoid this disease, mulch, rotate crops, pull up any volunteer potatoes that sprout from old tubers in the ground, and plant certified disease-free seed potatoes.

Carrot rust fly: If your carrots' roots have holes bored into them, they may be infected with carrot rust flies. The adult flies lay their eggs on the soil near carrot plants, and then when the young larvae hatch, they tunnel into the soil to feed on the carrot roots. If your carrots have these holes in them, you can eat the carrots as long as the disease hasn't started rotting the root.

To avoid this problem, rotate crops, grow resistant varieties, and cover the plants with a floating row cover (a cheesecloth-like material that lets air, water, and sun in, but keeps bugs out; see Chapter 21).

Colorado potato beetle: The most destructive potato pests, these 1/2-inch-long, tan- and brown-striped adult beetles lay yellow eggs in clusters on the undersides of potato leaves, starting in early summer. After the eggs hatch, the dark-red larvae feed on the leaves and can quickly destroy your crop (see Figure 6-4).

Control these insects by growing resistant varieties, crushing their eggs on sight, handpicking the young beetles, mulching with a thick layer of hay to slow their spread, and spraying the biological spray Bt ‘San Diego', which is specifically designed to kill young potato beetles but doesn't harm other insects, animals, or people, on the larvae. Potatoes can withstand significant potato beetle leaf damage and still produce. You just won't receive as large of a crop.

Onion maggot: This pest's larvae attack the bulbs of developing onions, causing holes, opening the bulb to infection from disease, and making them inedible. Onion maggots like cool, wet weather. To control onion maggots, place a floating row cover over young seedlings after the weather warms to around 70 degrees. Doing so prevents the adult flies from laying eggs on the young plants.

Potato scab: This fungal disease causes a potato's skin to turn brown with a corky texture. Tubers with potato scab are unattractive but still edible. Control this cosmetic disease by planting resistant varieties and rotating your crops.

Wireworm: These jointed, hard-shelled, tan-colored, 1-inch worms feed on underground tuber roots as well as the bulbs of a number of crops. They're generally a problem with recently sodded soil. Control this pest by setting potato traps before your root crops begin maturing. Spear a potato piece on a stick and bury it 2- to 4-inches in the ground; the wireworms should infest the potato piece. Dig up the piece after 1 week and then destroy it.