Horseradish in Zone 4a & 4b
Armoracia rusticana
Yes, horseradish grows in zones 4a and 4b. Plant it outside May 22–May 29.
When to plant horseradish in zone 4b
Zones 4a and 4b share the same average frost dates, so this page covers both.
Method: Direct sow: Direct-sow outside. It doesn't transplant well, or doesn't need the extra time indoors.
| Start indoors | Not typically started indoors |
|---|---|
| Direct sow / transplant outside | May 22–May 29 |
| Estimated harvest | Nov 18–Nov 25 (~180 days after direct-sowing) |
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 2-3 ft.
Plant alongside it in zone 4b
These go outside within two weeks of horseradish in zone 4b, so one planting day can cover them.
- TomatoMay 29–Jun 5
- Bush BeansMay 22–May 29
- Sweet CornMay 22–May 29
- CucumberMay 22–May 29
- ZucchiniMay 22–May 29
- Winter SquashMay 22–May 29
Horseradish is a perennial root crop grown from root cuttings rather than seed, and once planted, it tends to stay planted; any small piece of root left in the ground resprouts, which is both the plant's appeal and the reason gardeners give it a spot it won't outgrow its welcome in.
How horseradish fits zone 4's season
Zone 4b's frost-free window runs about 128 days, from May 15 to September 20. Horseradish needs about 180 days from sowing to first harvest.
Horseradish planting windows in every zone
Zone 4b is highlighted. Useful for comparing against a neighbouring zone, or for a garden somewhere else.
| Zone | Start indoors | Sow or plant out | Harvest |
|---|---|---|---|
| 3a & 3b | Not usually | Jun 6–Jun 13 | Dec 3–Dec 10 |
| 4a & 4b (your zone) | Not usually | May 22–May 29 | Nov 18–Nov 25 |
| 5a & 5b | Not usually | May 17–May 24 | Nov 13–Nov 20 |
| 6a & 6b | Not usually | May 2–May 9 | Oct 29–Nov 5 |
| 7a & 7b | Not usually | Apr 17–Apr 24 | Oct 14–Oct 21 |
| 8a & 8b | Not usually | Apr 1–Apr 8 | Sep 28–Oct 5 |
| 9a & 9b | Not usually | Feb 22–Mar 1 | Aug 21–Aug 28 |
Harvest dates are about 180 days after the sow or plant-out date.
Good companions
- Potato: The most commonly repeated potato companion, credited with deterring the Colorado potato beetle. As with the claim that marigolds deter potato beetles, no extension or research source was found testing horseradish against this specific pest: treat it as garden tradition, not measured evidence.
Where to buy horseradish seeds
None of the seed suppliers we list carries horseradish seeds right now. A local garden center or a specialty seed house is the place to look.
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing horseradish" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 4b calendar · Plan your beds in the Garden Designer →
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Growing Horseradish in USDA zone 4b: when to start seeds indoors, when to direct-sow, and when to expect a harvest.
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