Early May is the time to sow outdoor cucumbers, marrow, squashes, pumpkins (vertically on edge, not laid flat like a surf board) French and Runner beans and Sweetcorn in gentle heat around 20C in peat substitute seed compost or multipurpose compost individually in 7.5cm pots, ready for planting out once the danger of frost has passed. If the weather remains changeable, keep sowing salads for transplanting to keep producing, whatever the weather.
Pot up plug plants into small pots as soon as they arrive, label with the name and date of sowing and water them well. Repot on a cloudy day if you can or shade them for a few days until the plants establish. Buy larger plants from the garden centre, like aubergines and peppers for earlier cropping
Continue to prick out and pot on seedlings, gradually increasing the pot by one or two sizes each time until they reach the final pot size for plants like aubergines or chillis which are being grown on in the greenhouse. If not, repot as needed until they are ready for ‘hardening off’.
Outdoor plants need ‘Hardening off’ before transplanting. This will take two to three weeks, depending on the plant, the temperatures at which kept while in the greenhouse and the location of the garden. Hardy plants acclimatise more rapidly than half-hardy or tender plants.
Transfer plants from heated to cooler conditions on a cloudy day, or cover them with newspaper or fleece at first to protect them from scorching or wilting.
Put your plants at the base of a sheltered south facing wall or hedge during the day and protect them for the first few days with a couple of layers of fleece. Bring them indoors at night. Cover them with a single layer of fleece for the first part of week two. After about 10 days, depending on the weather, remove the fleece during the day and leave plants outdoors at night if it’s mild. Leave them uncovered day and night towards the end of the third week, before finally planting out. Timing is critical: tender plants should not be planted out until after the last frost in your area. Listen to weather forecasts and have cloches, fleece or newspaper ready, should late frosts catch you out. Tender plants can be damaged if hardened off below 12C(54F), Petunia, lobelia, Tagetes need consistent temperatures around 10-12C (50-54F), tender bedding like pelargoniums and Bizzy Lizzie, can be planted when minimum night and day temperatures are 10C (50F) and 14-16C (57-61F) respectively.
Keep a look out for glasshouse red spider mite, whitefly and other pests, check the underside of leaves and treat with environmentally friendly sprays before infestations become established. Increase the humidity around plants by misting with soft tepid water to discourage red spider mite which dislike dry air. Planting French marigolds in the greenhouse discourages whitefly but this should be done before an infestation occurs.
It is not too late to make two more sowings of runner beans in mid- May to extend the cropping season.
Happy gardening, Matt