The Best Unusual Roots to Grow in Delaware

Salsify, scorzonera, parsnip, celeriac, Jerusalem artichoke and horseradish are the safest unusual roots for Delaware. They tolerate cold, and they fit a season that runs well past six months at the reference weather station. Tender tropical tubers such as oca and yacon are the gamble. What follows sorts the choices by type and explains where Delaware’s humid summers and its spread of hardiness zones change the call.

The short answer for Delaware

Choose by type rather than by variety name. Hardy taproots (salsify, scorzonera, parsnip), perennial tubers (Jerusalem artichoke, horseradish) and fall-sown radishes such as daikon are the best fits. Celeriac and Hamburg parsley are good too, if you start transplants instead of direct-sowing.

The numbers explain why. In the NOAA 1991-2020 Climate Normals for the Wilmington airport station, the 30-70% probability band for a 32F freeze falls between April 3 and April 14 in spring. In fall it falls between October 26 and November 7. Those are probabilities of a freeze, not promises. They also come from one airport, so suburban and rural gardens usually see the last spring frost one to two weeks later and the first fall frost one to two weeks earlier. The mean daily minimum of the coldest month at the Wilmington reference station is 25.6F, about six degrees below freezing. The USDA Plant Hardiness Zone Map (2023) puts Delaware at 7a to 8a.

That combination favors roots that sit in the ground through the cool end of the year. A parsnip or salsify root that spends its last month in near-freezing soil converts starch to sugar and tastes better for it. Those same roots shrug off a winter whose typical coldest nights stay just below freezing, especially under a few inches of mulch.

For sowing dates inside those windows, see When to Plant Unusual Roots in Delaware. The broader overview sits in Growing Unusual Root Crops in Delaware.

What will not work here

Spring-sown daikon and black radish are the most common failure. They are cool-season crops, and a Delaware spring warms fast enough that the roots turn woody or bolt before they size up. Sow them in late summer and let the cooling soil do the work.

Parsnip and salsify fail for the opposite reason, which is germination. Both are slow, and parsnip seed can take weeks to come up. A bed sown in warm soil and watered once a week will crust over and dry out between waterings, leaving gaps. Salsify seed also loses viability quickly, so last year’s packet is a poor bet. Keep the seed row evenly damp until the seedlings show, or lay a board over it and check daily.

Humid summers punish close spacing. Celeriac packed tightly stays wet and shaded, which suits the leaf spots that thrive in Delaware’s muggy July and August. Give each plant room, water the soil instead of the leaves, and pull any spotted lower foliage. Heavy clay makes it worse. A root that meets a compacted layer will fork, and a forked salsify is nearly impossible to peel.

The tender tubers are where wishful thinking costs the most. Oca, yacon and mashua want a long run of frost-free weather, and oca in particular forms tubers late, as days shorten. With a first fall frost band of October 26 to November 7 at the airport station, and earlier in suburban and rural spots, a cold snap can kill the tops before the tubers have bulked up. That is a coin flip, not a plan. They also cannot overwinter outdoors when the coldest month averages a 25.6F minimum, so any you grow must be dug up and stored. Treat them as an experiment in a corner of the garden, not as the main crop.

Then there is the plant that fails by succeeding. Jerusalem artichoke, once established, returns from every tuber you miss. Put it where you can live with it, ideally in a bed with a hard edge.

What changes across Delaware

Delaware is small, but it is not one garden. The USDA Plant Hardiness Zone Map (2023) lists the state as 7a to 8a, so there is no single answer. The span includes 7b in between, and the zone is built on one variable only, the average annual extreme minimum temperature. It says nothing about summer heat, soil, or how long your fall lasts.

The soil shifts as much as the cold does. Northern New Castle County sits on the Piedmont edge, where soils run heavier and rockier. Much of Kent and Sussex counties is Coastal Plain, with sandier, easier-draining ground. Long taproots love the sandy side, since the roots run straight with little effort. In heavier northern soil, sow into raised beds or loosen the soil a full spade depth, and favor shorter roots such as celeriac, Hamburg parsley or a stubby parsnip type.

Gardeners in the cooler, more inland parts should treat the airport frost figures as optimistic. Add a week or two to the spring date, subtract the same from the fall one, and lean toward the hardy types that do not mind a short squeeze. Coastal and southern gardens often have milder winters and a slightly longer fall, which gives the borderline crops, oca and yacon, a better chance. Even so, the map is the authority here, and the pattern is a tendency, not a rule.

Which zone applies to your property is something this page cannot tell you. Look up your ZIP code on the USDA Plant Hardiness Zone Map and read the zone for your exact location. Then compare it with the reference-city figures used above and adjust.

Where to check this for your own county

The best next stop is University of Delaware Cooperative Extension, the state’s land-grant extension service. This page gives you a state-level picture built on one reference station. A county recommendation beats it, because the extension staff know your county’s soils, pests and frost pockets.

Look for two things. First, a local planting calendar for your county, ideally one that lists fall root crops separately from spring ones. This page does not carry a county-by-county calendar, and I would rather say so than guess. Second, any variety trials or recommended lists for your area. Trials show which cultivars handled Delaware’s humidity and disease pressure instead of just the seed catalog’s promises. Many gardeners skip this step, then wonder why the “heat tolerant” variety they bought still bolted.

If the website does not answer a specific question, such as whether yacon is worth trying in your part of the state, contact the county office and ask. Extension staff and Master Gardener volunteers field these questions all the time. Take along a note on your soil type (sandy, loamy or clay) and roughly when you see frost on the lawn. Those two details let them give an answer that fits your yard.

Checking this against your own garden

Your own observations outrank every date here. Three are easy to make, and none needs an instrument.

• Soil warmth by feel. Push your bare hand two or three inches into the bed in the morning. If it feels cold and clammy, parsnip and salsify seed will sit and sulk. If the top inch is dry and hot by afternoon, a shaded or mulched row will hold moisture better.
• First true leaves. Seedlings first show seed leaves, then the first true leaves with the plant’s real shape. How soon they appear tells you how fast your soil warms. Slow, uneven emergence points to a cool or crusting spot.
• The first frost on your own lawn. Note which corner whitens first on a clear fall morning. That low spot is your frost pocket. Keep tender tubers out of it, and compare the date with the October 26 to November 7 band, remembering that rural yards often freeze earlier.

Write the dates down for a couple of seasons. A simple notebook turns a state-level estimate into your own calendar, and it will start to disagree with this page in useful ways.

Common questions

What is the easiest unusual root to grow in Delaware?

Jerusalem artichoke and horseradish are the least fussy, because both are perennial and cold-hardy. Both also spread, so give them a dedicated bed. Of the annuals, salsify is a good first try if you can keep the seed row damp.

Can I grow oca or yacon in Delaware?

It is possible but marginal. They need a long frost-free season, and Delaware’s first fall frost band at the reference station is October 26 to November 7, earlier in many suburban and rural yards. They also will not survive winter in the ground, so plan to lift and store them.

Do unusual roots need to be harvested before winter?

Not the hardy ones. With a coldest-month mean minimum of 25.6F at the Wilmington reference station, parsnip, salsify, scorzonera and horseradish can stay in the ground under mulch and be dug as needed. Lift the tender tubers before a hard frost.

Is the frost date on this page right for my yard?

Probably not exactly. It comes from one airport weather station, and gardens outside the city usually see later spring frosts and earlier fall ones by one to two weeks. Check with University of Delaware Cooperative Extension and your own frost pocket.