Transplanting is the moment a seedling leaves the shelter of the windowsill and has to survive in the real garden — wind, sun, cold nights, slugs and soil that is nothing like the potting mix it grew up in. It is also the moment when the most young plants are lost, because a seedling put out too early, without hardening off, or planted badly, rarely recovers. Spring transplanting done well is a short, careful process: harden the plant off, choose the right day, plant it at the right depth, water it in, and protect it for its first week. This guide explains each step.
Timing: after the last frost, and not before
Tender transplants — tomatoes, peppers, courgettes, cucumbers, beans and tender flowers — must wait until the last frost has passed and night temperatures are reliably above 50 degrees Fahrenheit. A single frost kills them, and cold soil stunts them even if it does not kill them outright. Hardy transplants — lettuce, brassicas, onions and hardy flowers — can go out earlier, weeks before the last frost, as long as they have been hardened off. Use your local frost average as a guide, not a promise: plant tender crops a week or two after the average last frost, because half of all years have a frost after the average date. Your local extension service publishes frost averages for your area, and the frost date calculator can help you work out your window.
Soil temperature matters as much as air temperature. A transplant put into cold, wet soil sits and sulks, its roots unable to grow, and it is an easy target for slugs and disease. Wait until the soil has warmed and dried enough to crumble in your hand — see our spring soil preparation guide for the test. In zones 11 to 13, where there is no frost, transplanting is governed by heat rather than cold, and the best time is the cooler part of the day.
Hardening off before transplanting
Hardening off is the gradual adjustment of indoor-grown seedlings to outdoor conditions, and it is the step most often skipped and most often regretted. A seedling raised in a warm, still room has thin leaves and soft stems; put it straight outside and it wilts, scorches and may die. Harden seedlings off over seven to fourteen days: put them outside in a sheltered, shady spot for a few hours on the first day, bring them in at night, and increase the time outdoors and the exposure to sun and wind each day. By the end they should spend the whole day outside and, if nights are mild, the night too.
Water seedlings well before they go out, and do not harden them off on a windy or very cold day. A cold frame or sheltered porch is ideal, because it gives protection while letting the plants feel the temperature and the breeze. Our spring seed starting guide explains how to raise the seedlings, and our spring planting guide explains the order of spring planting.
How to transplant step by step
Choose a cloudy day, or plant in the evening, so the transplant does not face full sun in its first hours. Water the seedlings thoroughly an hour before transplanting, so the root ball holds together and the plant is hydrated. Prepare the planting hole in advance, water it, and set the plant at the same depth it was growing in its pot — with two exceptions: tomatoes can be planted deeper, because they grow roots along the buried stem, and brassicas can be planted slightly deeper for stability. Most other plants must never be planted deeper than they were growing, because buried stems rot.
Tease the seedling gently out of its pot, supporting the root ball, and never pull it by the stem. If the roots are circling the bottom of the pot, tease them out gently so they grow into the surrounding soil. Set the plant in the hole, fill around it with soil, firm gently with your fingers, and water thoroughly until the soil is wet all the way down. A watering can with a fine rose is best, because a hard jet washes the soil away from the roots. Mulch around the transplant to hold moisture — see our spring mulching guide — but keep mulch away from the stem.
Aftercare: the first week matters most
The first week after transplanting decides whether the plant establishes or fails. Water daily if the weather is dry, because the small root ball dries out fast and the roots have not yet grown into the surrounding soil. Protect the transplant from cold nights with fleece or a cloche, and from strong sun and wind with a temporary screen if the weather turns harsh. Watch for slugs, which eat young transplants overnight — see our spring pest control guide — and protect vulnerable plants with collars or barriers.
Do not feed a transplant until it is growing strongly, which usually takes two to three weeks: fresh soil contains nutrients, and fertiliser on stressed roots causes burn. Do not move a transplant again once it is planted, and do not disturb the soil around it. New growth is the sign that the transplant has established. If a transplant wilts in its first days, water it, shade it, and give it time — most recover within a few days if the roots are intact. If it does not recover, check your local extension service for advice.
Common transplanting mistakes
The mistakes, in order of damage done, are: transplanting before the last frost; skipping hardening off; planting in cold, wet soil; planting too deep; letting the root ball dry out before planting; watering too little in the first week; and feeding immediately after transplanting. A transplant that is leggy and weak is a poor candidate for transplanting at all — it is better to sow again or buy a stronger plant than to put a weak seedling out and hope. Handle seedlings by a leaf, never by the stem, because a crushed stem kills the plant. And label every transplant, because seedlings of different varieties look alike and it is easy to lose track of what is planted where.
Frequently asked questions
When can I transplant seedlings outdoors in spring?
Tender seedlings after the last frost, when nights are reliably mild. Hardy seedlings can go out weeks earlier, once they have been hardened off.
How long should I harden off seedlings?
Seven to fourteen days, increasing the time outdoors and the exposure to sun and wind each day, until they spend the whole day outside.
How deep should I plant a transplant?
At the same depth it was growing in its pot, except tomatoes, which can be planted deeper. Never plant a seedling deeper than it was growing, or the stem rots.
Should I water after transplanting?
Yes, water thoroughly immediately after planting, so the soil settles around the roots, and water daily in dry weather for the first week.
Why did my transplant wilt and die?
Probably transplant shock from no hardening off, cold soil, frost, drying out, or slugs. Harden off, wait for warm soil, water well and protect the plant. If you are unsure, check your local extension service for advice.