In Pennsylvania, plant the hardy unusual roots (salsify, scorzonera, parsnip) as soon as the soil can be worked, around the late-March to early-April frost window. Hold the tender ones until that window is well behind you. The dates below describe Philadelphia, the mildest corner of the state, so most of Pennsylvania should shift later.
The short answer for Pennsylvania
Start with what the dates are. NOAA’s 1991-2020 Climate Normals for the Philadelphia reference station put the last spring frost at March 29 to April 6 and the first fall frost at November 5 to November 16. Both are probabilities of a 32F freeze, not calendar guarantees. Each window is the band where the odds of a freeze sit between 30 and 70 percent. On March 29, a freeze still has a real chance of showing up. By April 6 it is closer to a coin flip going the other way. (The data is published by NOAA NCEI if you want to check the underlying figures.)
That window turns into a sowing calendar by type. The gap between the spring and fall windows is about seven months, which is generous for most roots but leaves little slack for the slowest ones. Here is how the common unusual roots line up against it:
| Type | Examples | When to plant, relative to the frost window |
|---|---|---|
| Hardy, direct-sown | Parsnip, salsify, scorzonera | Sow as soon as the soil is workable, in the March 29 to April 6 band or just after |
| Hardy tubers | Jerusalem artichoke | Plant early in spring, before or during the window |
| Long-season, started indoors | Celeriac | Start seedlings indoors ahead of time, transplant once the window has passed |
| Frost-tender | Oca, yacon | Plant only after the window closes, with a safety margin |
This page does not have a dated day-count for each crop, so the table works from frost behavior rather than days to maturity. For variety choices within each type, see The Best Unusual Roots to Grow in Pennsylvania. For the broader picture, see Growing Unusual Root Crops in Pennsylvania.
The winter number matters too. The mean daily minimum of the coldest month is 26.0F at the Philadelphia reference station. That is an average overnight low, not a record, but it is the figure that decides hardiness. Hardy roots left in the ground there face winter nights that average just below freezing, which parsnips and salsify handle. Tender roots do not. Plan on lifting the tender ones before the fall window opens.
What will not work here
The most common failure is planting by the calendar instead of the odds. A warm stretch in the third week of March tempts people to set out tender roots, and the March 29 end of the frost window says a freeze is still a live possibility. A single freeze is enough to finish seedlings of anything frost-tender. Hardy roots shrug it off. Oca and yacon do not.
Second, the tender tropical roots run out of runway in the colder parts of the state. The Philadelphia dates leave about seven months between the spring and fall windows, and that already assumes you plant at the safe end of the spring window. Move to the northern tier or the Alleghenies, where spring runs two to four weeks later, and the season shrinks by that same amount at the front end. This page does not have fall frost dates for those areas, so a northern gardener should not assume the fall window moves with them. What is certain is that the late start eats into any root that needs the whole season to size up.
Third, leaving tender roots in the ground over winter does not work. With a coldest-month mean minimum of 26.0F even at the mildest reference point, soil in most of the state will not hold tropical tubers through the winter. Mulch is not a fix for an entire zone mismatch. Treat oca and yacon as lift-and-store crops, and treat sunchokes and parsnips as the ones you can leave in place.
Fourth, late fall sowing of hardy roots is a gamble. Seed sown too close to the first fall frost window of November 5 to November 16 may germinate, then stall at seedling size as the cold arrives. A tiny parsnip in November will not become a usable one by December. Sow in spring, not as a rescue plan in autumn.
Last, the page has no summer heat or rainfall figures for Pennsylvania, so it cannot tell you how humid July will be. What it can say is that cramming roots close together tends to be a mistake in any season. Crowded rows give fungal leaf problems an easier time and hold the roots back. Use the spacing printed on the seed packet rather than squeezing in extra.
What changes across Pennsylvania
Pennsylvania is not one garden. The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places the state across zones 5a to 7b. That is a spread of about ten zone steps of difference between the coldest and mildest corners, depending on how you count half-zones, and it means there is no single answer for the whole state. The USDA system rests on one variable only: the average annual extreme minimum temperature. It says whether a plant survives winter. It does not say when to plant it.
The dates in this article belong to Philadelphia, which is the mildest corner. The northern tier and the Alleghenies run two to four weeks later in spring. A reader there should push every spring date in the table back by that amount: the hardy-root sowing, the celeriac transplants, the tender-root planting. Altitude works the same way. Higher ground warms later, and low pockets where cold air settles can hold frost after the surrounding slope has cleared.
The zone spread also changes what you can leave in the ground. In the milder end of the range, hardy roots overwinter easily and tender ones are still lift-and-store crops. At the colder end, even hardy roots may need a thick mulch layer, and the margin for tender crops is thinner because of the shorter season. For your own zone, check the USDA map directly. This page will not tell you which zone you are in, because the answer depends on your address and, within the same county, on your elevation.
Where to check this for your own county
Your state land-grant extension service is the right next stop. For Pennsylvania, that is Penn State Extension. Extension offices work at county level, and county staff see what actually grows in the local soil and climate, which a statewide article cannot.
When you get there, look for two things. The first is the local planting calendar for vegetables: sowing and transplanting dates tied to your county’s frost pattern, not Philadelphia’s. The second is the list of varieties trialled in your county or the nearest research site. A variety that does well in a southeastern trial may stall in a northern one, and the trial results show it.
This page does not have a Penn State root-crop calendar in its facts, so it cannot point you to a specific document. It also does not borrow calendars from other states. Extension services in other states publish calendars for their own climates, and those dates do not transfer. If a county page and this page disagree, believe the county page. A county recommendation beats a state one, and this page is the state one, built from a single reference station that happens to sit in the mildest corner of Pennsylvania.
If you call or email your county office, ask about the earliest safe sowing date for hardy roots, and whether anyone locally has grown oca, yacon, or salsify. Local growers who have already failed at something are a better guide than any table.
Checking this against your own garden
Your own observation outranks every date on this page. Three things are worth watching, and none needs equipment.
- Soil warmth by feel. Push a hand into the bed. If the soil feels clammy and cold against your skin, it is not ready for the tender roots. A bed on a south-facing slope that feels warm weeks before a shaded one is telling you about your microclimate.
- The first male flowers. Catkins on maples, hazels, or alders, or the earliest male flowers on squash if you grow it, show how early your yard is running. If your trees are blooming before the neighbors’ down the road, you may be warmer than the regional average.
- The first true leaves. Sow a short test row of something quick, such as radishes. When the true leaves, the second set after the seed leaves, show up, the seedlings are establishing in your soil. Slow, yellowish growth means the bed is colder than the calendar suggests.
If all three say you are behind the Philadelphia dates, believe them. A garden at higher elevation or in a frost pocket can run weeks behind a reference station, and your plants will tell you more than any chart.
Common questions
Can I sow parsnips or salsify in March in Pennsylvania?
In the milder southeast, the hardy roots can go in once the soil is workable, which overlaps the March 29 to April 6 band. In the northern tier or the Alleghenies, wait: spring there runs two to four weeks later than Philadelphia.
What do the frost dates on this page actually mean?
They come from NOAA’s 1991-2020 normals for the Philadelphia reference station and mark where the chance of a 32F freeze is between 30 and 70 percent. They are probabilities, not guarantees. A freeze after the window is still possible, just less likely.
Does my hardiness zone tell me when to plant?
No. The USDA system looks only at the average annual extreme minimum temperature, so it tells you what survives winter, not when to sow. Pennsylvania spans zones 5a to 7b, so check the USDA map for your own location.
Which roots can stay in the ground over winter?
The hardy ones, such as parsnip, salsify, scorzonera, and Jerusalem artichoke, can generally stay, since the mean daily minimum of the coldest month is 26.0F even at the mildest reference point. Oca and yacon are the ones to lift before the fall frost window opens, which starts November 5 in Philadelphia and can arrive earlier in colder parts of the state.