Hartley Magazine

All the latest news, hints, tips and advice from our experts

‘Hardening off’ plants

‘Hardening off’ is the process of acclimatising plants which have been grown indoors, until they become robust enough to grow outdoors for the summer like bedding plants, ornamental or vegetable seedlings propagated in the greenhouse and tender or half hardy plants, like Fuschias and dahlias, which have been protected through the winter. It usually takes two to three weeks and should be carefully timed, so tender plants are not planted out until after the last frost in your area. It is worth listening to the forecast and having temporary protection like cloches, horticultural fleece or newspaper close to hand, so late frosts don’t catch you out.

One of the easiest ways to ‘harden off’ is to put plants in a warm, sheltered part of the garden, covered with horticultural fleece (two layers may be necessary if it is cold or windy) at the base of a south facing wall or hedge, for example, once temperatures have risen, during the day, putting them back into the greenhouse at night. Do this for two weeks, before uncovering them during the day on week three and finally planting out, in week four.  Growth is checked and the leaves turn yellow if they become too cold, too quickly.

It is also important at this time of year to inspect plants regularly for signs of pests and diseases – daily if you can, as they’re much easier to control, before they become established. If you are growing lilies, the curse of the lily beetle may already be in your garden. Both the orange-red bodied adults and the larvae, which have the nasty habit of hiding under a glob of black excrement, strip Lilies and Fritillaria’s of their foliage and flower buds overnight, leaving an horrendous mess and an angry, disappointed gardener. Pick off adults by hand, cupping one hand underneath to catch them in case they fall – their defence mechanism is to drop from the plant as you reach to pick it up. Lifting plants in pots and shaking them, gently over an umbrella or plastic sheet is a way of catching them, too, as the orange-red beetles are obvious against a white background.

Vine weevils are active too, nibbling notches out of the leaf margins at night, their white and c-shaped, larvae with pale brown heads, feed on the roots of containerised plants, so plants suddenly wilt and die.  They can be controlled using a biological control nematode, Steinernema kraussei or the imidacloprid or thiacloprid as a spray, drench or bought mixed into the compost. The beetles hide in darkness during the day, so check under pots or staging in the greenhouse, lay sheets of hessian, old tiles or black plastic, or loose rolls of corrugated paper, tied with string or a rubber band, as traps, then pick off the adults and crush them. Mulch pots with a layer of gravel, or put gauze over the drainage holes, to prevent females from laying their eggs, or apply sticky barriers, such as petroleum jelly or insect barrier glue, around the rims of pots or glasshouse staging. Encourage predators, such as birds – robins love the larvae; frogs, toads, shrews, hedgehogs and predatory ground beetles happily eat them too. Don’t let them beat you! Happy gardening!