Rhubarb in Zone 4a & 4b
Rheum rhabarbarum
Yes, rhubarb grows in zones 4a and 4b and comes back each year. Plant it outside May 1–May 8.
When to plant rhubarb 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 1–May 8 |
| Estimated harvest | First real harvest in year 3 |
Spacing: about 10 square feet per plant (square-foot-gardening spacing). Mature height: 2-3 ft.
Before you plant: Rhubarb has a winter-hardiness note for zone 4b. See the details below.
Plant alongside it in zone 4b
These go outside within two weeks of rhubarb in zone 4b, so one planting day can cover them.
- RadishApr 17–Apr 24
- CarrotApr 24–May 1
- LettuceMay 1–May 8
- BroccoliMay 1–May 8
- Flower SproutsMay 1–May 8
- Gai Lan (Chinese Broccoli)May 1–May 8
Rhubarb is a perennial vegetable, though it's used like a fruit in the kitchen, and it's one of the more patient long-term investments in a garden: the crown planted this spring won't give a harvest for a few years, but a well-sited planting can then keep producing for a decade or more.
How rhubarb fits zone 4's season
Zone 4b's frost-free window runs about 128 days, from May 15 to September 20. Rhubarb takes about 2 growing seasons to reach first worthwhile harvest, so what matters here is how many of these seasons it gets, not whether one is long enough.
Rhubarb is hardy in zones 3-8, so in zone 4b it stays in the ground through winter and comes back rather than being replanted. Allow about 3 ft of spread at maturity.
Rhubarb 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 | May 16–May 23 | First real harvest in year 3 |
| 4a & 4b (your zone) | Not usually | May 1–May 8 | First real harvest in year 3 |
| 5a & 5b | Not usually | Apr 26–May 3 | First real harvest in year 3 |
| 6a & 6b | Not usually | Apr 11–Apr 18 | First real harvest in year 3 |
| 7a & 7b | Not usually | Mar 27–Apr 3 | First real harvest in year 3 |
| 8a & 8b | Not usually | Mar 11–Mar 18 | First real harvest in year 3 |
Good companions
- Cabbage: Traditional companion pairing that makes good use of the space around rhubarb's large leaves.
- Onion: Alliums planted nearby are traditionally paired with rhubarb without competing for space.
Where to buy rhubarb seeds
True Leaf Market (each supplier's rhubarb seeds)
Varieties we recommend, and where to get them:
- 'Victoria': Wisconsin Extension describes this as a speckled type, medium stalks with light green color developing pink speckling toward the base, a visually different look from Valentine's solid color rather than a color that necessarily cooks better. Buy: True Leaf Market Full notes
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See it growing
Search YouTube for "growing rhubarb" 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 Rhubarb in USDA zone 4b: when to start seeds indoors, when to direct-sow, and when to expect a harvest.
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