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Rhubarb is a long lived perennial. A crown planted well will still be cropping in ten or fifteen years, and every one of those years depends on decisions you make in the hour before it goes in the ground. There is no second chance to improve the soil under a crown once it is planted.
Give it full sun if you can, though it will take half a day of shade and simply crop a little later. What it will not take is standing water. A crown sitting in a wet hollow through winter rots from the middle out, and the first sign is usually a whole plant that fails to come up in spring. If your ground stays sodden after rain, plant on a low mound six inches (15 cm) high rather than in a hole.
Keep it out of the middle of the vegetable beds. The leaves reach three feet (90 cm) across in high summer and shade everything around them, and you do not want to be digging or rotavating near the crown every year. The edge of a plot, or a bed of its own, suits it far better.
| Requirement | What to aim for | What happens if you get it wrong |
|---|---|---|
| Light | Full sun, or at least half a day | Thin, pale stalks and a slow crop |
| Drainage | Water gone within an hour of heavy rain | Crown rot over winter |
| Soil pH | 6.0 to 6.8 | Sluggish growth on very acid ground |
| Winter cold | Several weeks below 40F (4C) | Weak spring flush without proper dormancy |
| Space per crown | Three feet (90 cm) in every direction | Crowded, spindly stalks and more disease |
Dig in more than you think it needs
Rhubarb is one of the hungriest things in the garden and it feeds from the same square yard for its whole life. Work well rotted manure or mature compost into a patch about two feet (60 cm) across and a full spade deep before planting. A bucketful per station is not too much. Break up any compacted layer at the bottom of the hole while you are down there, because the roots go far deeper than most people expect.
Pull out every scrap of perennial weed root while the ground is open. Once the crown is established you cannot dig around it without cutting into its roots, and couch grass or bindweed running through a rhubarb crown is close to impossible to remove afterwards. Spend the extra twenty minutes now.
Do not add fresh manure directly against the crown itself. It holds moisture around the buds and invites rot. Mix it through the soil, and keep the top inch immediately around the bud clear.
Setting the crown at the right depth
Plant while the crown is dormant, either in late autumn once the leaves have died back or in very early spring before the buds move. A dormant crown is a lump of woody root with one or more fat pink buds on top, and the whole job is a matter of getting those buds at the correct height.
- Dig a hole wider than the crown Make the hole broad enough that the roots spread out sideways rather than being folded down into a column. Sit the crown on a small mound of soil in the center so the roots run downhill away from the bud.
- Set the buds just below the surface On free draining soil, cover the buds with about an inch (2 to 3 cm) of soil. On heavy or wet ground, leave the tips of the buds level with the surface or barely proud of it. Buried too deep in cold wet soil, the buds rot before they ever push through.
- Firm and water in Firm the soil with your hands rather than treading it hard, then water thoroughly to settle it around the roots. If autumn planted and the ground is already wet, one watering is enough.
- Mulch around, not over Spread two inches (5 cm) of compost in a ring around the crown, leaving a clear gap of a couple of inches around the buds themselves. This keeps the moisture where the roots are and the air where the buds are.
- Mark the position Push a cane in beside the crown. Rhubarb disappears completely over winter and it is easy to put a fork through a dormant crown while tidying the bed.
If you are planting a container grown plant in leaf rather than a dormant crown, keep the top of its rootball level with the surrounding soil and water it every few days until new leaves appear.
The first year: take nothing at all
This is the single hardest instruction to follow and the one that decides whether you have a strong crown or a struggling one. In the first growing season after planting, pull no stalks whatsoever. Every leaf is feeding the root system, and a crown stripped in its first year spends the next three seasons catching up.
In the second year you can take a light picking, no more than three or four stalks from any one crown, and stop early. From the third year onward the crown will carry a full season of pulling. If a flower spike appears in either of the first two years, cut it out at the base immediately.
Write down the planting date and the exact position of each crown, and note which year each one becomes a full cropping plant. In five years time, when one crown is producing half what its neighbor does, that record tells you whether it is age, position or how hard you picked it.