Gardening: Tips and tasks for greenhouse growing in the height of summer

Expert Matthew Biggs offers advice on how to keep your glasshouse plants in tip top shape...

Make sure to keep your greenhouse well ventilated when it's very warm
By Hannah Stephenson, PA

IF YOU have a greenhouse, the likelihood is it will be pretty warm in there over the summer, particularly with the extreme temperatures we’ve been having.

So, how do you stop your plants wilting, make sure your fruit and veg are thriving and halt greenhouse pests in their tracks during the hot summer months?

TV garden expert Matthew Biggs, gardening writer for historic glasshouse manufacturer Hartley Botanic (, offers the following advice:

1. Keep it ventilated: “When temperatures run high, watering and ventilation are top of the list. Open greenhouse vents early in the morning, as temperatures will soon rise (you should also have some form of shading in place by now), water preferably in the evening or early morning and check plants several times a day to ensure that they don’t dry out.”

2. Be waterwise: “Consider using ‘grey’ water from the shower, bath, kitchen or from washing machine rinse cycles on ornamental plants in the greenhouse,” he suggests. Keep detergent levels like shower gel to a minimum and don’t store grey water for longer than 24 hours. Softened tap and dishwasher water are useful, but only as a very temporary measure and water containing bleach and disinfectants are a ‘no no’, of course.

“It is at times like these when past efforts you put into collecting rainwater really pay off so don’t waste it. Water at the base of the plant around the roots, not over the leaves, learn to estimate how much each pot needs and store your watering cans under the greenhouse bench to catch any drips draining through. When you carry the can from tap to greenhouse you are more careful with the water you use.

“Keep your greenhouse pots and borders weed free, so the plants, not weeds, use the water and when the rains arrive again, flush out the compost with fresh, unadulterated rainwater.”

3. Keep your cool over edibles: Keep twining cucumber stems round their supports and cut back the side shoots two leaves beyond the flowers and fruits, to increase airflow and reduce chances of mildew – keeping foliage dry, the plants well-watered and mulching also reduces the risk of mildew.

“It is well worth growing resistant varieties like ‘Carmen’, ‘Passandra’ and ‘Bella’. Harvest cucumbers when fruits are about 30cm long and water with high potash fertiliser to encourage further fruiting.

“Feed fruiting crops like sweet peppers and chillies according to the manufacturer’s instructions, continue removing side shoots from tomatoes, tap the open flowers to encourage pollination and tie the stems to canes or supporting string as they grow. Keep the compost moist as erratic watering causes splitting and ‘blossom end rot’.”

4. Keep control of pests: “Check regularly for signs of pests, like whitefly and red spider (or ‘two spotted’) mite. Before introducing biological controls use environmentally friendly sprays containing fatty acids, plant invigorators, plant extracts or plant oils as others leaving chemical residues will kill them.

“Whitefly can then be controlled using Encarsia formosa, red spider mite by increasing humidity around the plant or introducing predators like the mite Phytoseiulus persimilis.

“To maintain hygiene, keep the greenhouse free from damaged or diseased material and sweep the paths as plant debris can harbour pests and diseases, it looks more professional, too and when you have finished all of this, sit out in the garden and enjoy the sunshine.”

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