After ice saints (May 15): which frost-tender plants to plant out

TL;DR

After May 15, the ice saints have passed and frost risk drops below 5%. Heat-loving plants like tomatoes, peppers, aubergines, basil, and summer flowers can now go outdoors safely. Transition goes smoothly when you harden gradually: first in dappled shade for a few hours, then full day outside, then into the ground. Check your weather forecast just in case, as late frosts are rare but not impossible.

The moment after ice saints: why now?

The ice saints (May 11-15) are historically the last frost dates of spring in Western Europe. After this period, overnight frost risk drops below 5%. For gardeners, this marks the safe window to move frost-tender plants from your warm propagation bed or windowsill outdoors.

But "after May 15" does not mean "throw everything outside on May 16 and go home." The temperature shock between your indoor seedling area (20-22 degrees daytime, 15 degrees night) and outdoors (10-12 degrees night in late May) can damage tender plants. This process is called "hardening off" or "acclimatization."

Frost-tender plants you can now plant: tomatoes, peppers, aubergines, basil, oregano, tender mints, courgettes, pumpkin, melons, sweet potatoes, and all tender annuals (petunias, marigolds, salvia, zinnias).

Step 1: Prepare hardening off (days 1-3)

Begin hardening at least 3-5 days before planting out. This is not optional. Plants moved directly from your warm house to 10-degree nights suffer transplant shock and grow weakly or die.

Days 1-2: Put seedlings outside for a few hours in dappled shade (under a tree, north-facing wall). No direct sunlight. Temperature difference: 15-18 degrees. Duration: 2-3 hours daily. Keep soil moist. Bring them in before evening.

Days 3-4: Now place them a few hours in dappled shade, then 2 hours gentle sun (morning/evening). The plant adjusts photosynthesis to outdoor light (more intense than windowsill light). Still no overnight outdoors.

Day 5: Full day outside in dappled shade (8 hours). Still bring in for the night.

After these 5 days your plants are "hard enough" for the ground.

Step 2: Plant into the ground

After hardening, you can carefully plant seedlings into the garden. Timing: late May in prepared planting holes with rich, loose soil. Tomatoes for example: hole filled with compost, deep planting (until first leaves touch soil), support stake in place immediately.

TL;DR how to plant: dig hole, gently tease apart root ball (do not tear), place plant, firm soil around it, water thoroughly.

First week outdoors: Shade young plants from harsh midday sun with netting or cloth. Basil tolerates less shade than tomato, but avoid brutal afternoon sun.

Step 3: First week baby care

First week after planting: water daily in morning. Soil stays moist but not waterlogged. Tomatoes are thirsty: once planted, they draw water rapidly. In dry May, water generously in morning.

Feeding: Tomatoes, peppers, courgettes gradually gain strength after planting. After 2-3 weeks apply organic tomato fertiliser (soluble, weekly). Herbs like basil need less feeding.

Disease prevention: Keep foliage dry (water at the base, not overhead). Frost damage symptoms: brown leaves, wilting, no growth. Very rarely happens after May 20, but if you get a night below freezing (unlikely), cover plants overnight with frost cloth.

Quick reference: which plant, which date, which timing?

• Tomatoes (standard): After May 15, harden 5 days, plant out.
• Tomatoes (cherry): After May 10 (earlier, hardier).
• Peppers & Aubergine: After May 20 (more frost-tender, wait longer).
• Basil & Oregano: After May 15. Basil is tender, not earlier.
• Courgettes & Pumpkin: After May 15, harden 3 days enough.
• Summer flowers (Petunia, Zinnia, Salvia, Marigold): After May 15, harden 3-5 days.
• Sweet potato (seed potatoes): After May 20, warm soil desired (at least 16 degrees).

When in doubt, wait until May 20. Better late than dead.

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Step-by-step

Step 1: Harden days 1-3

Place seedlings 2-3 hours daily outdoors in dappled shade (check soil moisture).

Step 2: Harden days 4-5

Full day outside in dappled shade. Bring inside for night still.

Step 3: Plant out after day 5

Prepare planting hole, loosen root ball gently, plant to first leaves, firm soil, water well.

Step 4: First week care

Water morning, no feeding yet. Shade from hot sun.

Frequently asked questions

Can I plant tomatoes out on May 16?

Not without hardening. Moving directly from your warm windowsill to full outdoor conditions kills tender plants. Minimum 3 days acclimatization, but 5 days is safer.

What if frost comes after May 15?

Very rare in Western Europe after May 20, but possible in unusual years. If forecast shows a night below freezing: Cover plants with frost cloth or old sheets overnight. Do not leave them permanently covered, as they need light.

My basil is thin and pale. Will it do better outside?

Yes. Indoor basil gets insufficient light at home. Once outside (after hardening), it grows faster and tastes better. But hardening is essential, otherwise soft foliage scorches in full sun.

How much water after planting out?

Daily if dry. Soil feels moist 5 cm deep. Not waterlogged. Tomatoes want lots, basil less. Feel with your finger: dry? Water. Wet? Wait.

Are warm crops really frost-tender until May 15?

Yes. One night at 0 degrees and your whole tomato bed dies. After May 20, risk drops below 2%, so practically zero. For tomatoes, peppers, aubergine: wait until May 20 and sleep soundly. For courgettes and flowers: May 15 is okay.

Discover your own May garden

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