The recent spate of warm weather shouldn’t prompt gardeners to plant out tender plants just yet, because late frosts can still do their worst, Hannah Stephenson warns
It’s so tempting, I know. All those annuals you’ve sown indoors from seed are now big enough to plant out, the tomato seedlings are doing well and you just want to clear those windowsills, the greenhouse or the conservatory to make a head start on summer.
But be warned, if you risk planting tender plants out before the last frosts have passed, it could ruin all your hard work of the previous months.
Depending on where you live, a late frost can hit in late May or even in June, reducing your tender plants to shrivelling corpses, so it’s prudent to be cautious about planting out or removing protection too early and to plant tender bedding plants out after the danger of frost has passed.
It’s best really to sow seed of frost-tender vegetables including French and runner beans, courgettes, marrows, cucumbers, tomatoes, squashes and melons, in April under cover because they are going to take four or five weeks to establish before they can be put outside, so that way they are timed to be planted out after the last frosts are over.
Anything grown in a frost-free greenhouse such as patio plants and frost-tender vegetables will need hardening off before being planted outside, to acclimatise them slowly to outdoor conditions. Harden them off two to three weeks before planting.
They can be hardened off in a cold frame or simply moved outside into a sunny, sheltered position during the day and then brought back inside at night.
For new tender plants which are already in the ground but need some protection, cloches are always a good idea and can be removed during the day when the temperatures rise.
Protect new shoots and fruit tree blossom with horticultural fleece and cover plants in an unheated greenhouse with newspaper.
If spring frosts have affected tender young growth, causing scorching and pale brown patches to appear between the leaf veins, often on the exposed and top edges of the plant, don’t give up just yet as the plant may still be alive. Many plants can be surprisingly resilient and may well rejuvenate from dormant buds at or below soil level. This takes time so recovery may not be seen until early summer. If the plant is of high value or it is not essential to fill the gap, consider leaving the damaged plant in the ground until mid-summer. If no re-growth has appeared by then, replace it.
If you want to plant up hanging baskets early with young plants, make sure you take the baskets under cover at night, keeping them in a sheltered porch or similar area. Troughs and patio tubs which you want to plant up with vulnerable plants should also be treated similarly, or covered at night with horticultural fleece.
Frost problems are often made worse where plants face the morning sun, as this causes them to defrost quickly, rupturing their cell walls. Periods of cold, frosty weather during April and May can also kill blossom and damage fruit. Camellia and magnolia are particularly vulnerable and can be ruined in a single frost.
Avoid planting tender plants in frost pockets, which tend to be at the lowest point in a garden, as cold air and frost always descend and settle at the lowest point. Instead, plant them in a sheltered spot, under large trees and shrubs or against walls, to give them some heat and protection in winter.
And don’t give up just yet if your plants succumb to frost - if you wait till early summer you may see some signs of growth underneath the damaged parts and can cut back the dead growth to give the new growth a chance to catch up.