Root vegetables: The underground garden
April 26, 2010
  • /Crop Sciences
Although the stars of most vegetable gardens are tomatoes, peppers, beans, cucumbers and squashes, it's time to shed a little light on the ones that grow underground, said a University of Illinois Extension horticulture educator.

"The 'root crops' are vegetables such as carrots, radishes, beets, parsnips, salsify, turnips, and rutabagas," said Stack.

"Most all of the root crops have similar cultural requirements and grow best in cool weather. In addition, the tops of some of these crops such as beets and turnips are commonly used as cooked greens and can be harvested while plants are young."

Proper soil preparation is the key to success with root crops. They grow best in a deep, well-prepared, loose soil that retains some moisture but is well drained.

"To achieve this, work in ample amounts of organic matter when preparing the soil," he said. "Compost and well-rotted manure are excellent sources of organic matter. Put on several inches and work it into the soil.

"Also, applying about one-half to one pound of general purpose fertilizer per 100 square feet of bed area will take care of the fertility needs of the crop. Another way to achieve a good seed bed for these crops is to build up the bed 8 to 10 inches. This provides for a loose, open soil that allows the roots of these crops to develop to their fullest."

Beets are a native of the south coast of Europe and are known as beet root, blood turnip, and beet-rave (beet-radish). Beets are fairly frost hardy and can be planted about 30 days before the frost-free date in your area.

"Successive plantings at three- to four-week intervals should be planned to ensure a fairly constant supply of fresh, young beets," said Stack. "Plant just enough at each sowing to satisfy your needs for fresh beets. To ensure quick germination, beet seed can be soaked in warm water overnight prior to planting.

"Also, because beet seeds are actually many seeds clustered together, it is important to thin after they emerge to ensure quality roots. If you want, you can delay thinning of the seedlings until they reach three to four inches tall and use the tops of the thinned plants cooked much like spinach. Beets grow best when supplied with uniform soil moisture."

While many gardeners plant red varieties such as 'Ruby Queen' and 'Detroit Dark Red,' there are other colors available. 'Golden' is a yellow rooted beet, and 'Chioggia' has an interior that is colored red and white like a candy cane. 'Lutz's Green Leaf' is an heirloom variety that is good for a fall harvest and winter storage. While it gets large, it does not lose its flavor and quality. Carrots are another cool-season root crop that grows best when planted in early spring as soon as the soil can be worked. Midsummer planting using short-season varieties such as 'Thumbelina', 'Minicor' and 'Little Finger' often yield excellent, tender, sweet carrots for a fall harvest.

"Because carrot seed germinates slowly, a single radish seed planted every six to 12 inches in the row with the carrot seed will help to mark the row," he said. "Later plantings benefit from a uniformly moist seed bed.

"As with all root crops, thinning is important to achieve quality carrots."

Suggested spacings are two seedlings per inch of row if they will be harvested when young and about one seedling per inch for large varieties such as 'Danvers', 'Chantenay' and 'Imperator.' Summer-planted carrots can be left in the ground until after a killing frost for late harvest. In many cases, a heavy mulch of straw placed over the row allows carrots to be harvested well into the winter. This is a great way to extend the harvest.

If orange is not your favorite color, you may want to grow 'Atomic Red,' a brilliant red carrot or 'Belgian White', 'Snowhite', or 'Luna White', which are excellent white rooted carrots, Stack noted.

Parsnips are grown as a full-season vegetable and valued for their long, white root resembling a white carrot. Parsnips are considered a winter vegetable because their flavor is not fully developed until the roots are exposed to near freezing temperatures for two to four weeks in the fall and early winter. During this time the starches change to sugars, resulting in a sweet nut-like flavor.

Parsnips are sown in early May. Because they are slow to germinate, many gardeners will sow both radish seed and parsnip seed in the same row at the same time, a technique called intercropping. The radishes are quick to germinate and help mark the row and break the soil crust. In about 20 to 25 days, the radishes can be harvested, leaving room for the parsnips to continue growing to maturity.

"Parsnips should be left in the garden until the tops freeze in the fall," he said. "To make harvesting easier, gardeners often mulch the row with straw, making harvesting easier through the winter."

In the spring, before new growth begins, the roots can still be harvested, and it is at this time that both the flavor and quality are at their best. 'Sugar Hollow Crown' and 'Harris Model' are suggested varieties.

"Radishes are an ancient crop that came from China and were cultivated by the Egyptians and Greeks. They are perhaps the easiest and quickest root crop to grow," Stack said.

"Planting can start as soon as the soil can be worked in the spring, making successive, short row plantings every 10 to 14 days to ensure a supply of quality radishes. Additionally, proper thinning and growing radishes 'fast' with ample moisture contributes to good-looking and good-tasting radishes."

For later maturing radishes, consider the fall or winter radishes such as daikon or black radish. The daikons are often large, long white roots, and the black radishes are round (three to four inches) with a rough black skin. These tend to be excellent storage types. The winter radishes need extra growing time and are best planted in mid-summer.

Spring radish varieties such as 'Cherry Belle', 'French Breakfast', 'Sparkler', and 'Champion' can also be replanted in the fall as weather starts to get cooler. There are many more varieties of radish to choose from with a color and shape to please just about every taste. Winter radish varieties include 'Round Spanish Black' and 'Chinese White'.

"Turnips and rutabagas are both frost-hardy cool-season vegetables that are often used as substitutes for potatoes," he said. "Turnips are easily grown and mature in about two months. They can be planted in the spring, late summer or early fall for harvesting as either roots or for the tops as greens. Fall planting often results in a better-quality crop.

"Rutabagas take about four to six weeks longer to mature and are best grown as a fall crop. The roots are large, round, and firmer than turnip."

Salsify is a European favorite grown since the 13th century and carries the curious name of vegetable oyster because the cooked roots have an oyster flavor. Salsify is a creamy white root that looks like a carrot with tiny hairs growing on the outside.

"There is also a type of salsify known as 'Scorzonero' that produces black skinned roots," he explained. "Salsify is grown in much the same way as parsnips, sowing the seed in early spring in a well prepared rich soil for best root development. Salsify is a true perennial and is able to withstand freezing temperatures."

It can be harvested any time you can get a shovel into the ground. Covering the row with a straw mulch makes the job of late-season harvesting easier. Another interesting note is that if the roots are allowed to remain in the garden until spring, the young shoots that emerge in the spring are often harvested and eaten like asparagus.