“How can I tell when an underground veggie (onion, potato, etc) is ready to harvest. I have tried growing onions and I get large green growth above ground and there is basically a marble-sized onion bulb underneath — or smaller!” Question from Naomi of Oakdale, California
Answer: It’s an excellent question. In most cases, it is pretty easy to tell because most root crops bulb up at the top. You can expect this to happen with beets, onions (see image below), radishes, turnips, and rutabagas. It also happens to carrots and parsnips, though sometimes their bulbous tops are less prominent.
Potatoes, sweet potatoes, and garlic are different matters. These tuberous (or bulbous in the case of garlic) crops remain underground, so you need to gauge how the plants up top are growing to determine harvest time. Here are guidelines for harvesting each.
Potatoes: “New Potatoes can be harvested as soon as the plants begin to bloom. Wait for larger potatoes. These can be harvested after the plants have fully died away. You can harvest all of your potatoes at this time for storage, or just harvest them as needed. Be sure to get them all out of the ground shortly after the first frost of the season. Otherwise, they will develop an unpleasant sweet flavor.” (Click here to read the full Ask a Garden Expert.)
Sweet Potatoes: “Sweet potatoes are harvested 90-120 days after transplanting or immediately after a frost has blackened the tops of the plants.” (Click here to read the full article.)
Learn how to grow beautiful beets from seed to harvest. With a little know how, they are one of the easiest root vegetables to grow in the garden. (Germination is faster if you soak beet seeds for one night before planting in the ground!)
Root crops are the finest vegetables for the fall garden. Specialty varieties of carrots, beets, and turnips have been bred just for fall and winter growing and storage. Once the first frost hits, they sweeten up for better flavor. If properly stored, they keep beautifully through winter. Cold-frame gardeners can also rely on them for consistent winter production.
There’s a reason why root-rich stews, roasts, and soups are favored in colder months. These vegetables are superior winter keepers that taste the best in the late-season cool weather. That’s why they have been in constant cultivation for thousands of years across Eurasia. They provided needed food and nutrition when no other fresh vegetables were available. Today’s gardeners also reap the benefits of carrots, beets, and turnips with the added advantage of superior varieties for taste, texture, and performance.
Carrots (Daucus carota) are available in lots of colors. Classic orange carrots originate from Europe and tend to be the crispest and sweetest. Purple or red carrots were initially cultivated in the Middle East, Russia, and India and are stronger-tasting and less sweet. All types can be grown as winter carrots, but some perform better than others.
True winter carrots are exceptionally cold hardy, long tapered, often slower to mature, and remain crisp and sweet through the winter months. The heirloom orange varieties ‘Imperator 58’ (75-days, 1933 All-America Selections Winner) and ‘Danvers 126’ (70 days) are two excellent choices favored by gardeners for decades. Newer winter keepers that remain tasty in storage are the slender orange ‘Interceptor’ (120 days), super sweet ‘Napoli’ (58-days), and super keeper ‘Dolciva’ (105-days).
Favored for centuries by Eurasian gardeners living in colder climates, beets (Beta vulgaris) are very hardy and will keep for months. Beets for winter growing are exceptionally hardy and stay smooth and sweet without getting fibrous and woody. Their tops can also be eaten like Swiss Chard. Lots of classic red beets are beautifully suited to cold-weather growing.
The slow-to-mature heirloom ‘Lutz Winter Keeper’ (80 days) was first developed in the 1800s and has proven to be a great selection for fall gardens, yielding large, red beets with good flavor that store very well. Another old-time winter beet is ‘Detroit Dark Red’ (55 days). The classic mid-American variety has uniformly round roots with good sweetness.
Beets prefer a neutral pH and do not grow well in acid soil, so add lime to beet beds if your garden soil is acidic. Next, amend with Black Gold Garden Compost Blend for increased fertility. Before planting beets in the ground, soak the seeds overnight for faster germination. Varieties that take longer to produce should be started no later than early September.
Beet seeds have 2-3 embryos, which means a single seed can yield two or three seedlings, encouraging more seedling clumps that require thinning. For easier thinning plant the single-embryo variety ‘Moneta’ (46 days), which produces just one seedling. Its red beets are also delicious and great for fall and winter cultivation. (Click here to see our video about growing beets!)
Turnips (Brassica rapa) are members of the mustard family (Brassicaceae) along with other cole crops like cabbage, which is why their roots have a sweet cabbage-like flavor. Their slightly bitter greens are also edible.
Historians determined that humans first began to eat turnips in prehistoric times. The easy root crops were grown and eaten by the Greeks and Romans, and in India, they were raised for their flavorful, oil-rich seeds. Turnips are also important to East Asian culinary traditions.
The old-time ‘Purple Top White Globe’ (50 days) is the classic turnip that most gardeners grow. The white roots have electric purple tops, and the young leaves are favored in the South for turnip greens. For something unique, try the red-rooted ‘Scarlet Ohno Revival’ (50 days) turnip, which can be eaten fresh or cooked. The white-rooted Japanese variety ‘Tokyo Market’ (35 days) has a fruity, sweet flavor ideal for eating fresh in salads.
Grow in fertile loam with a neutral to slightly alkaline pH of 6.5 to 8. These are faster growing, so gardeners can wait until early October to sow seeds in fall gardens or cold frames.
Storing Root Vegetables through Winter
Homeowners used to have root cellars for keeping produce through cold months. The humid cellars maintained roots at optimal storage temperatures between 32 and 40 degrees Fahrenheit. These days we have refrigerators, but if you have a large harvest, you’ll likely need more storage space. Here are four smart, space-saving ways to store your root harvest in winter. (Always remember to remove the greens from your root crops before storing them!)
Provide Garden Cover: This easy method allows gardeners in milder winter areas to keep their crops in the ground. Before hard freezes hit, cover your root crops with a 1- to 2-foot layer of straw. This will protect them from harsh cold and winter heave. Just uncover and dig them as you need them.
Grow in a Cold Frame: The best cold frames are stone or brick-lined, sunken, and plexiglass covered to hold in the heat from the winter sun. Topping cold frame crops with rich compost will add extra protection from cold and make winter harvest easier.
Dig a Root Clamp: This is an old way to store roots without a root cellar. Dig a broad hole about 3-feet across and 1 or 2-feet deep in your garden. Add a thick base layer of straw, layer in your roots, add another thick top layer of straw and cover the sides with a layer of soil and compost. Leave a chimney of thick straw at the top for protection and aeration. Dig in through winter when you want to gather roots for eating!
Create Root Box for a Cool Basement or Garage: If your basement or garage stays below 40 degrees Fahrenheit through winter, create root boxes! Take an aerated wooden or thick cardboard box, layer in straw and lightly moistened peat moss, and add moistened root crops between them. Then collect the roots as you need them.