For Massachusetts, the safest unusual roots are the hardy, patient ones: salsify, scorzonera, celeriac, Jerusalem artichoke, horseradish and burdock. They shrug off cold, tolerate a slow spring and sweeten after autumn frost. Heat-hungry tropical roots like sweet potato, yacon and oca are possible, but only on the mildest sites. The reasons come down to frost dates and winter cold.
The short answer for Massachusetts
Choose by type, not by variety name. Build the plan around cold-hardy roots, add long-season roots started indoors, and treat the tropical group as an experiment. That ranking comes from how much season the state offers, and the numbers are decent but not generous.
What the frost dates say
NOAA’s 1991-2020 Climate Normals, at the Boston Logan station, put the 30-70% probability band for a 32°F freeze between April 1 and April 8 in spring. In fall, that same band falls between November 3 and November 14. These are probabilities of a freeze, not promises. Around those dates, another freeze is still a real possibility in spring, or already a real possibility in fall.
Simple arithmetic on those dates gives roughly 209 to 227 days between the spring and fall bands at Logan. That is the best case. Logan is a waterfront urban station and the mildest spot in the state, so inland suburbs and the Berkshires frost later in spring and earlier in fall. This page does not have a season-length figure for those places.
What winter does
The mean daily minimum of the coldest month is 23.1°F at the Boston reference station. That is a monthly average, not a record low, and it explains why roots such as horseradish, Jerusalem artichoke and salsify can sit in the ground through winter with a mulch layer on top. Cold decides what survives. Season length decides what finishes.
| Type | Examples | Fit for Massachusetts |
|---|---|---|
| Hardy, overwinter in the ground | Jerusalem artichoke, horseradish, burdock, salsify, scorzonera | Strong. Cold is an asset, not a threat. |
| Long season, cool-tolerant | Celeriac, Hamburg parsley | Good when started indoors and transplanted. |
| Warm-season tropical | Sweet potato, yacon, oca | Marginal on the coast, riskier inland and at elevation. |
If you want only one row of the table to act on, take the first. Those roots turn the state’s cold season into an advantage, and the timing on the Growing Unusual Root Crops in Massachusetts overview builds on the same logic.
What will not work here
Direct-seeding celeriac in the garden fails. The seed is tiny and slow to germinate, and the plant wants a long, steady run of growth. Even at Logan’s roughly 209 to 227 days between freeze bands, an outdoor sowing leaves little margin. Inland, with a shorter run, the margin disappears.
Yacon is the clearest loser. It is a tropical plant that takes most of a long frost-free season to build its tubers. A grower who sets plants out after the last freeze and then watches the first fall freeze arrive will often dig small, disappointing roots. Oca has a different problem: it forms tubers as days shorten in fall, which is exactly when frost shows up. A Logan-style November 3 to November 14 window may leave time on the coast, but a frost weeks earlier in the Berkshires ends the crop while the tubers are still small.
Sweet potatoes sit in between. Slips set into cold spring soil stall, so they need black plastic or a late start, and a cool summer in the hills leaves them behind. Treat them as a coastal and southeastern bet.
The April 1 to April 8 band is its own trap. It describes the mildest station in the state, not your yard. Sowing salsify or parsley-type roots on those dates inland means seed sitting in cold, wet soil, where it rots or germinates unevenly. Seed in the ground early is not the same as seed growing early.
Humidity is the less obvious failure. Massachusetts summers are humid, and close spacing in a humid summer invites leaf disease on celeriac and mildew on Jerusalem artichoke stands. Crowd them to save room and you may lose the crop to foliage problems before the roots size up. Give celeriac generous elbow room and let air move.
Soil matters too. Stony ground is common across much of New England, and long, thin roots like salsify and scorzonera fork and split when they hit rocks. Loosen a deep bed or choose shorter-rooted types where the soil is rough.
Finally, winter harvest is not guaranteed. Roots left in the ground are safe from cold, but frozen soil inland can make digging impossible. Mulch heavily, or pull what you want before the ground locks up.
What changes across Massachusetts
The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places Massachusetts across zones 5a to 7b. There is no single answer for the state. That spread is wide, and it separates a high-elevation Berkshire garden from a Cape or island one.
Remember what that number measures. The USDA zone is built on one variable: the average annual extreme minimum temperature. It says whether a perennial like horseradish or Jerusalem artichoke survives winter. It says nothing about how long your season is or how hot the summer runs, and two gardens in the same zone can have frost dates weeks apart. Look up your own location on the USDA map rather than assuming a zone from a neighbor’s.
If you garden in the north or at altitude, shift your plan in four ways:
- Skip yacon and oca entirely.
- Start celeriac indoors earlier and transplant on the later side of your own frost date.
- Favor the hardy overwinterers, which lose nothing to a short season.
- Use deeper mulch on anything left in the ground.
If you garden near the coast, the warm-season experiments become reasonable, though the same site advice about spacing still applies. The sowing dates for each type are laid out in When to Plant Unusual Roots in Massachusetts, and they move with your location in the same way.
Where to check this for your own county
This page is the state view, and a county recommendation beats a state one. Frost dates, soil and rainfall change from county to county, and the people who know your county are the ones running trials in it.
Start with UMass Extension. Look for two things. The first is a local planting calendar for your area, ideally with frost dates stated for your county or the nearest town rather than for Boston. The second is any list of vegetable varieties trialled in your region, because a variety that finished well in a Berkshire trial tells you more than a catalog’s national claim.
Also check whether extension staff can help with a soil test and advice on drainage and stony soil, since those decide whether long roots grow straight. If a calendar for a particular crop is missing, ask the extension office instead of borrowing one from another state. This page does not have a Massachusetts extension calendar for these specific crops, and it does not substitute a neighbor’s.
Treat what you find there as the more precise layer. Use this page to decide which type of root deserves a bed. Use your county source to decide when to put it in.
Checking this against your own garden
Your own observation outranks every date above. The frost bands describe a station by the harbor, and your yard may run days or weeks different. Three things are worth watching, and none needs an instrument.
Soil warmth by feel. Push your hand a few inches into the bed in spring. If it feels cold and clammy, wait. Warm, crumbly soil that drains means seed will germinate, and a bed that warms days before a neighbor’s tells you it is a good spot for the warm-season experiments.
First true leaves. Sow a short test row of something quick, like radishes, and note when the first true leaves, the ones after the seed leaves, appear. Slow emergence means a cool site and a later start for celeriac transplants and salsify.
First frost bite. In fall, note which tender plants blacken first and where. Frost damage in the low corner and not on the slope shows you the cold pocket, so you can keep tropical roots out of it. An early blackening date, compared with the November 3 to November 14 band, tells you how much shorter your season is than Logan’s.
Jot the dates down for a year. They will serve you better than any state table.
Common questions
Can I grow sweet potatoes in Massachusetts?
Yes, on mild coastal or southeastern sites with warm soil and a late, patient start. Inland and in the hills the season is a gamble, so treat the harvest as a bonus.
Can I leave unusual roots in the ground over winter?
Hardy types such as horseradish, Jerusalem artichoke, salsify and scorzonera can stay in the ground. With a coldest-month mean minimum of 23.1°F at the Boston reference station, cold is not the problem. Frozen soil inland can be, so mulch heavily or harvest before the ground locks up.
Should celeriac be started indoors?
Yes. The seed is slow and the plant needs a long run of growth, so a transplant gives it the head start the season can’t. Time the move outdoors to your own last frost, not Logan’s April 1 to April 8 band.
Is Jerusalem artichoke a safe first choice?
It is among the most dependable roots here, and that is the catch. It spreads from any tuber left in the soil, so plant it in a contained bed you can dig thoroughly each year.