11:06 - 12 May 2010
May can be a bit of a dilemma in the greenhouse. It’s a fabulous month for the gardener because everything is growing vigorously, but for the greenhouse gardener it is often the month that they realise they should have bought a bigger greenhouse. That’s because by May every available space on the benches, staging, shelving and floor is covered in pots and trays and modules and even growing bags full of burgeoning plants. For the plants that will remain in the greenhouse for the whole season such as the indoor tomatoes, chillies, aubergines, cucumbers and more, their space is allocated and acceptable. But for the other tender plants that are simply waiting to go outside, it can seem an interminable wait for the greenhouse gardener.
Keep all plants well spaced so that air can circulate freely between them.
Ventilate. It’s vital to keep good airflow within the glasshouse and to keep the temperature below 75F if possible. That means on sunny days you need to make sure the windows are open and that there is a good flow of air. Ideally you need floor level vents and roof vents so that cold air is drawn in low down and released through the roof when it has warmed up. If it is really hot leave the door open during the day but be sure to barricade it against cats and dogs and other creatures that may cause havoc inside.
If you can’t regulate the greenhouse temperature, you need to think about shading the glasshouse. Fit greenhouse shades or blinds, ideally these should be on the outside of the greenhouse and should cover the south facing glass. You can use a special greenhouse shading paint that can be rubbed off after the summer or internal fabric shades that can be fitted to the greenhouse frame.
Daily watering is now essential. If you aren’t able to do this then use self-watering trays, micro-irrigation connected to a timer and a tap or employ the help of a friend or neighbour. Water in early evening so that your plants get the full benefit of the water.
All the plants in containers, pots, modules and growing bags are totally dependent on the nutrients contained in the growing medium they are growing in. By now they will have used up most of this and will need supplementary feeding. Flowering and fruiting plants need a fertiliser rich in potash so look for a high K level on the NPK content that is listed on the pack. Plants that need good, green and strong foliage need a high Nitrogen content so look for a high N level on the NPK content that is listed on the pack.
Raise the humidity in the greenhouse by filling bowls of water around your space and damping down the floor in the morning.
Carry on sowing. Most plants sown now will be large enough and strong enough to plant outside after the last frost.
Keep [potting up all plants as their roots fill the pots they are growing in.
Sow herb seeds such as sweet basil, parsley and chives. Grow them in small pots containing top quality seed compost.
Sweet corn, courgettes, marrows, squash and other tender plants can be sown with protection towards the end of May. Sow into individual modules, small pots or into Root Trainers to give the plants plenty of room to develop and mature.
As the season progresses and your vegetable sowings start to mature you can start to harvest early sown salad crops, carrots, radish, beetroot and other developing vegetables. Where possible remove alternate plants to leave plenty of room for the remaining plants to develop.
As other crops start to mature in quick succession, keep up with the harvest. Vegetables such as peas, mange tout; runner beans and courgettes will be more productive if the crop is harvested regularly.
Plant out established seedlings of leeks, Brussels sprouts, summer cabbage, cauliflowers and celery.
Ensure that newly transplanted vegetable and fruit plants are kept well watered while they establish.
Pinch out the side shoots of cordon tomatoes as they form. If the side shoots have become quite large then treat them as cuttings and root them in a gritty cuttings compost to increase the number of plants that you grow. Tie in your plants as they develop, especially as fruit starts to form or they will quickly topple over and be damaged.
When the first tomato flowers start to form mini fruits, feed the plants. Use a dedicated tomato food.
Pot up individual tomato plants into larger pots in the greenhouse or plant up three tomato plants into a deep growing bag. This also applies to cucumbers, aubergines and peppers, which can all be grown in pots or Instant planters indoors or out according to their variety. Check your seed packet for more information.
Don’t allow tomato plants to dry out. Stress, inconsistent watering and a lack of calcium can lead to split fruits and blossom end rot. A dedicated Tomato Food will contain vital trace elements to reduce the risk of this disfiguring disease.
Plant out other established plants such as runner beans, sweet corn, courgettes, squash and others when they are large enough to handle and when all danger of frost has passed.
Sweet corn, courgettes, marrows, squash and other tender plants can be sown in the greenhouse or even into the garden during June. For the best results sow seed into individual modules, small pots or into Root Trainers to give the plants plenty of room to develop and mature. Plant them out when they are large enough to handle.
