By the end of the month frost will have passed from just about everywhere, allowing tender bedding plants such as petunias, begonias, African and French marigolds and busy lizzies (Impatiens) to be planted out to the garden or containers.  Before then it is a good idea to let them gradually become accustomed to outside conditions by ‘hardening off’ the young plants for a week or two so the move to outdoor conditions does not give them too big a shock when they are transplanted to their flowering positions.  To begin with bring trays of plants out of the greenhouse during the day and take them back in during the evening, remembering to protect them with fleece, bubble-wrap or sheets of newspaper. 

After a week or so, begin to leave them outside at night as well, unless frost is forecast when they should again be taken back in.  By the end of May you should have fine, sturdy, well hardened young plants ready to put on a great display of colour all summer long and in to autumn.

In the fruit garden, place straw or strawberry mats under strawberry plants so that as the fruits begin to ripen next month they will not become splashed with mud when it rains. Unprotected strawberries are a great treat for wild birds, which will always beat you to the ripening harvest.  Best to cover the crop with a fine mesh netting, although old net curtains will do at a push! 
Apply a liquid feed to spring bulbs after they have flowered, to encourage repeat flowering next year, and to help prevent ‘daffodil blindness’.  Allow the foliage of daffodils and other spring-flowering bulbs to die down naturally.  This allows the bulbs to build up their reserves, which are lost if the foliage is cut back while still green. Remove faded wallflowers and other spring bedding from the garden and containers, to make space for summer plantings.  These can be added to the compost heap, along with grass cuttings as lawns really start to grow this month, often needing a weekly mow.
Vine weevil larvae are serious pest of containerised plants, and become active from May onwards.  Tip out the rootball of suspect plants, and inspect for the creamy, orange-headed grubs, which tend to curl up into a ‘C’ shape. There are various chemical and biological controls available.  If they go unchecked they will feed on the roots and cause affected plants to suddenly keel over as all the roots have been eaten.  Aphids multiply rapidly during mild spells. Remove early infestations by hand to prevent the problem getting serious. Look out for them particularly on sweet pea plants, as they causes viruses in the young plants.
In the greenhouse, remove side-shoots from tomatoes growing as cordons up strings or canes.  Check every day and even them we are sure that, like us, you will still manage to miss one or two.  It is an important job because these side-shoots sap the strength and cropping potential of the plants.
Out on the vegetable plot or allotment, earth up potatoes:  Draw up soil around their stems when the shoots are 9in high, so the tubers do not become green and inedible. This simple process may need to be done a couple of times as the plants really put on growth through the month.  Remember to keep making ‘little and often’ sowings of salad crops such as spring onion, radish, lettuce and other salad leaves to ensure a continuity of supply through the summer months.