The time of sowing and transplanting depends on soil and air temperature: most fruiting and root crops are started after frost risk, above 15 °C. Leaf crops and herbs tolerate the cold and can start earlier.
Sowing and transplanting: the rules from the dataset
- Avoid root stress. The first rule of sowing and transplanting: transplant with the root ball intact and don’t damage the roots.
- Plant at the same depth. Put the plant at the same depth it grew at in the previous container: planting it too deep can rot the stem base.
- Harden off 5–7 days. After transplanting, the plant needs a few days to settle: protect it from full sun and water regularly.
Direct sowing or transplanting
Some plants (radish, lettuce, herbs) are sown directly in the pot, avoiding transplanting: radish, carrot and beet in particular tolerate moving poorly, and direct sowing is the route the dataset flags for them. Others (tomato, peppers) start in a seedling tray and are transplanted when they have 2–3 true leaves: the true leaves count, not the first two that come up from the seed.
The day of the transplant
For the transplant, pick a cloudy, windless afternoon and water well right after: the seedling should find the root ball already moist in the new pot. Check that the hole has enough room for the roots, without bending them: it is the most common mistake in small pots.
Hardening off: 7–14 days outside
Before moving seedlings permanently outside, they need gradual hardening off: start with a few hours out of full sun and, over 7–14 days, increase light and exposure. Bring them in at night, and on windy days or below 7 °C keep them inside: this is the move that reduces transplant shock.
The Sowing and transplant calendar tool tells you, based on plant and zone, the right period for sowing and transplanting in a pot.
Sources
- Royal Botanic Gardens, Kew — Plants of the World Online — taxonomy
- Royal Horticultural Society — plant care
- University of Maryland Extension — container growing
- University of Minnesota Extension — containers and climate
- Penn State Extension — urban container growing
- UMD — Hardening Off Vegetable Seedlings — hardening off
- UMN — Planting the Vegetable Garden — direct sowing and transplanting
