How to Transplant Seedlings Without Killing Them

How to transplant seedlings without killing them comes down to hardening them off, handling them gently and watering well, so the roots settle before the sun and wind arrive.

Move seedlings only when they are ready and the soil is warm enough, harden them off over 7 to 10 days, loosen any circling roots, plant at the right depth for the crop, and keep them shaded and evenly moist for the first few days. Do that and transplant shock is mild, short and mostly invisible.

This guide is for anyone moving seedlings from trays or pots into beds or containers. It covers readiness signs, hardening off, soil temperature, depth by crop, spacing, aftercare and what to do when seedlings sulk. It sits in the Plant Growing Guides guides and follows on from planting seeds step by step.

Transplanting at a glance

How to tell a seedling is ready

Age matters less than size. Look for two to four true leaves (the leaves after the first pair of cotyledons), a stem as thick as a pencil lead or more, and white roots showing at the drainage holes or holding the root ball together when you tip it out. Tomatoes are usually 15 to 20 cm tall, brassicas 10 to 15 cm. Plants that stay too long in small cells become root-bound: roots circle, the top turns purple or yellow, and growth stalls after planting. If you’re running late, pot seedlings on into larger pots rather than leaving them to starve.

Hardening off, day by day

Indoor seedlings have thin leaf surfaces and little wax. Sun, wind and cold nights scorch and shock them. Hardening off thickens the leaves and slows water loss before they face the open garden.

Tender crops such as tomatoes, peppers, basil and squash should come in whenever nights drop below about 10°C. Cabbage, kale, lettuce and onions tolerate a light frost once hardened. In a hot, dry climate focus on wind and midday sun, and use 30 to 50 per cent shade cloth. In humid tropical gardens, hardening is mainly about direct sun and heavy rain, so start under a tree or a veranda.

Is the soil warm enough?

A calendar date is a guess. Soil temperature at planting depth is better, and a cheap probe thermometer pays for itself. Take a reading at 10 cm depth in the morning.

The planting method

1. Water the seedlings an hour or two before lifting so the root ball holds together.
2. Dig the hole wider than the root ball and fill it with water. Let it drain, so the roots sit in moist, not dry, soil.
3. Release the plant. Squeeze the cell or pot and slide the plant out. Hold it by a leaf or the root ball, never the stem.
4. Loosen the roots. If roots circle, tease them apart with your fingers. If they form a solid mat, make three or four vertical cuts 1 cm deep with a clean knife.
5. Set at the right depth (see the table below) and fill around the ball with soil, firming with your fingers rather than your boot.
6. Water in slowly with 0.5 to 1 litre per plant, until a shallow basin is full twice.
7. Mulch 3 to 5 cm deep, kept clear of stems (see Mulching Mastery).

Planting depth by crop

Spacing and soil preparation

Crowded transplants compete from week one. Tomatoes need 45 to 60 cm, peppers 40 to 45 cm, brassicas 40 to 60 cm, lettuce 20 to 30 cm and squash 90 cm or more. Before planting, fork in a few centimetres of compost, but skip strong fertiliser, which burns damaged roots. If your ground is heavy clay or loose sand, check Understanding Your Soil Type before planting out a whole bed.

Peat pots and paper pots sold as “plant whole” often don’t break down fast enough. Tear off the rim above the soil, which otherwise wicks moisture away from the roots, and slit the sides. Coir and cardboard cell pots are more reliable.

Aftercare in the first two weeks

• Day 1 to 5: shade with a cloth, upturned pot or fleece from 11am to 4pm. Check moisture daily in warm weather.
• Day 5 to 14: remove shade, water deeply every 2 to 4 days, depending on soil and weather, instead of a daily sprinkle (see Watering Plants the Right Way).
• Protect from pests: slugs, snails, cutworms and birds all target fresh transplants. Use collars of card around stems and netting where birds pull plants.
• Feed after 2 weeks with a dilute liquid feed if growth has restarted.

Diagnosing a sulking transplant

Transplanting into containers and moving self-sown seedlings

For pots and tubs, use fresh potting mix rather than garden soil, and leave 2 to 3 cm between the mix surface and the rim so water has room to soak in. A single tomato wants at least a 20 to 25 litre container, a pepper 10 to 12 litres, and lettuce or herbs 3 to 5 litres per plant. See Choosing Pots and Potting Mix for material and drainage choices.

Self-sown seedlings from the garden, such as calendula, nigella or foxglove, move best when they have only two to four true leaves, before a taproot forms. Lift them with a spoon and a generous plug of soil, replant within minutes, and treat them like any other transplant. Larger seedlings with a long taproot rarely survive the move, so thin them where they stand instead.

Climate adjustments

• Cool-temperate: use cloches, fleece or black mulch to warm soil two weeks early, and plant tender crops on sunny, sheltered ground.
• Hot-dry: plant in the last 2 hours before sunset, water the evening before and after, and use shade cloth for the first week.
• Humid-tropical: plant at the start of a rainy spell but avoid the heaviest rain, and raise beds so roots don’t sit in saturated soil.

Why transplanting seedlings succeeds or fails

Hardening off toughens tomato and cabbage leaves, so the seedling loses less moisture when wind and sun reach it. A cloche or fleece protects young kale from frost, and a shade cloth reduces sun scorch on lettuce in the first week. Watering the tray first holds the root ball together and prevents the damage that stops growth after planting.

Transplanting at dusk or on a cloudy day cools the roots and reduces wilt, so you’ll lose fewer plants than at midday. Handle each seedling by a leaf and not the stem, because a crushed stem kills it while a torn leaf recovers. A trowel dug to the full depth of the cell encourages roots to spread, while compacted topsoil blocks them. Compost or mycorrhiza in the planting hole supports new roots, and a deep drink settles the soil around the cabbage or pepper. How long does it take to recover? Most seedlings pause for a few days, so you shouldn’t feed them until new leaves appear.

Making transplanting seedlings less of a shock

Tomato stems form roots along any buried section, so deep planting in loose topsoil improves anchorage and drought tolerance. Cabbage and lettuce prefer their crown level with the surface, because a buried growing point encourages rot and a raised one dries out. A paper or card collar 8 cm tall around each stem stops cutworm from severing it, and a grit barrier protects against slug and snail. Wait until soil temperature reaches 10°C for kale and 15°C for pepper and squash, because cold soil blocks phosphorus uptake and stalls the roots.

Space plants to the width on the label, usually 30 cm for cabbage and 45 cm for kale, since crowding spreads downy mildew between leaves. Water the tray before lifting so the compost holds the roots together, and a trowel lifts the whole ball without tearing it. Firm the soil gently with your fingers, give each plant 0.5 litre from a watering can and add a thin mulch, which holds moisture and removes air pockets that dry the roots. Shade cloth or a row cover for 3 days after planting reduces scorch and protects soft leaves from wind.

Don’t feed with fertiliser or urea for the first 2 weeks, because strong nitrogen pushes soft leaves before the roots can support them. Seedlings that sulk after you’ve planted them often just need a few days, but check the roots for root rot or damping-off before you worry. How to Plant Seeds Step by Step covers the sowing and compost choices that keep roots intact, and Watering Plants the Right Way controls drought stress afterwards. Your local extension service or the RHS can confirm the safe planting date, since late frost kills tender seedlings and tomato.

Mistakes to avoid

• Skipping hardening off because the weather looks mild
• Planting by date rather than by soil temperature
• Pulling seedlings out by the stem
• Burying peppers and squash like tomatoes
• Planting into dry soil and watering afterwards
• Giving strong fertiliser at planting

Seedlings raised indoors stay sturdier under a grow light, as shown in Grow Lights for Seedlings.

What to read next

For tomatoes, see How to Grow Tomatoes. To grow more plants without seed, try Propagation by Cuttings, and for timing, use the Seasonal Planting Calendar. Back to the Plant Growing Guides.