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Harden off seedlings of tender plants before you plant them out in the garden.

Geraniums, busy lizzies, petunias and the like are grown in hot houses that mimic the warm tropical climates from where they originate. They may be tropical in origin, but can put up with our cool nights, just as long as they don't feel the lethal finger of frost – May has already seen several night frosts, so it pays to be wary.

Place the pots or trays outside in a sheltered position where they can acclimatise to cooler conditions. A covering of a sheet of plastic at night will help them grow strongly during the next few days and give them some protection.

While you are waiting for this hardening process, prepare the soil where they are going to grow so that it is rich in organic matter and can hold the maximum amount of water.

Meanwhile, lilies should be growing strongly ready to burst into fragrant bloom next month. Unfortunately, they are all susceptible to attack from the scarlet menace – the lily beetle.

You may notice the first signs of small black lumps of mud moving around the plant eating foliage and stems. Underneath this mud are the larval stages of the pest that precede the adult beetle stage with pillar-box red wing coverings. The adults eat notches out of the edges of the leaves and lay more eggs that continue with the life cycle.

Spraying the larvae or adults with an ordinary insecticide does little to reduce the population, so it's best to opt for BugClear Ultra, an insecticide which is also effective against whitefly and greenfly.

Watch out for aphids (greenfly and blackfly) on roses, delphiniums, lupins, foxgloves and pansies. They can multiply with phenomenal speed, so a weekly check throughout the garden armed with a suitable hand sprayer is ideal.

Prune back spring-flowering shrubs such as forsythia, flowering currants and spiraea.

Tulips that bloom in May provide a difficult dilemma to tidy gardeners, who prefer to plant up bedding plants into an empty border. Should they dig them out or let them stay? The answer is, like so many in gardening, "it all depends".

If they have finished flowering, they can be dug up and replanted in a clump in a tucked-away moist soil spot where they can continue their life cycle, unnoticed but still growing. If you want to encourage these tulips to put on another great display in future years, however, you should leave their roots undisturbed and instead water and feed them while they are still in flower.

Just remove the flowered tulip stem after the petals have fallen and plant your bedding plants around the bulb foliage. They will die back in June and your bedding will grow into the remaining gaps.

YP MAG 29/5/10