SUMMER GREENHOUSE GROWING ADVICE
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Summer provides an opportunity to enjoy the fruits of your labour in the Greenhouse. Now is the time to
harvest and eat the delicious produce you have planned and cared for over the first half of the year. But,
there are still important jobs to do to maintain your Greenhouse’s productivity through the coming
months and ensure all your hard work is not lost through pests or disease. Hartley Botanic, England’s most
historic and respected Glasshouse and Greenhouse manufacturer has provided the following summer
Greenhouse growing advice. It’s online magazine also offers a wealth of know-how when it comes to
Greenhouse growing and ownership: Gardening Tips & News from Expert Gardeners – Hartley
Botanic (hartley-botanic.co.uk)
Summer sowing
August is the time to sow Fennel, oriental vegetables like mizuna greens and pak choi, rocket, coriander
dill, spinach, claytonia and land cress in modules as early in the month as possible. These will germinate
quickly and can be planted out by mid-August for cropping in autumn.
Continue sowing ‘cut and come again’ crops like mixed herbs, in pots, Greenhouse borders or growing
bags. Mixed salads can be started in shade under Greenhouse benching then moved outdoors. In late
August sow spinach, spring onions, lettuce and spring cabbage for transplanting and overwintering
outdoors. If the weather is hot, make sure you move seedlings outdoors immediately after germination,
protecting them with horticultural fleece from scorching sunshine and cold winds if it is a poor summer.
Start potatoes in time for Christmas
If you’d like to eat new potatoes at Christmas (or earlier), it is time to plant them now. Early potatoes,
stored in temperature-controlled conditions are sent out from late July to early August for immediate
planting. They can easily be grown in pots. Stand two or three tubers on a 12.5cm layer of multipurpose
compost in a 30m flower pot, then cover with a further 5-7.5cm of compost and water well. When the
shoots are 15cm high almost cover them with another layer of compost, continue to do this until the shoots are within 5-7.5cm of the top of the container, moving them into the Greenhouse before the first
frosts to stop the foliage from being damaged. Why not plant several pots? Some to be harvested earlier,
others left until Christmas. ‘Carlingford’ and ‘Charlotte’ are two varieties that are often offered. They can
also be ‘chitted’ and planted from late August to early September if space is short.
Cuttings
Take cuttings from semi ripe, non-flowering shoots of salvias and penstemons and pelargoniums from July
until mid-autumn, they should be 10-15cm long, making a cut just below a leaf joint. Trim off the lowest
leaves and pinch out the growing tip, then dip the cut end in hormone rooting powder, knock off the
excess then plant 3-4 around the edge of a 9cm pot, in multipurpose compost mixed with a little grit for
drainage. Keep the cuttings shaded in a Greenhouse propagator at 20degC. Once rooted move them into
7.5cm pots and keep them in the Greenhouse for planting out, after ‘hardening off’ the following year.
Summer pests and diseases
To reduce the chance of Blossom End Rot on tomatoes, peppers (and occasionally aubergines), keep the
Greenhouse well ventilated, keep the soil consistently moist, watering two or three times a day if needed.
This is particularly important when using growing bags as the compost is very difficult to moisten once it
dries out. Automatic watering systems, for larger pots up to 37.5cm in diameter, or growing in borders are
all helpful, especially where frequent watering is not possible; mulching around the roots helps, too. You
can still eat the tomatoes even if they have Blossom End Rot – just slice off and compost the damaged part.
Check aubergines, sweet peppers, cucumber, melon and chilli’s daily for red spider mite and whitefly which
can take hold from late spring and especially into summer. Use organic sprays containing plant oils or
extracts, fatty acids or plant invigorator to control red spider mite. Damping down and misting plants also
offers a measure of control but is not a long-term solution. Natural pyrethrum, fatty acids or plant oil
sprays help to control whitefly. None of these last long so regular applications will be needed to keep the
pests in check. Biological controls are also effective. Use the predatory mites Phytoseiulus
persimilis and Amblyseius the predatory midge (Feltiella acrarsuga) and a rove beetle (Atheta coriaria) for red
spider mite and Encarsia formosa for whitefly. These are available from your garden centre or online. Stop
spraying once biological controls are introduced.
And if you go on holiday…
If you are going on holiday, ask a gardening friend to check your Greenhouse daily, they can be paid in
harvested crops. If ripened fruits remain on the plant, they deteriorate, go to waste, attract disease and
stop cropping, shortening the harvesting season, so in the long term they are also doing you a favour. Fill up
the watering cans and put them under the Greenhouse bench to warm the water, for 24 hours before
leaving and give your neighbour written bullet point instructions, rather than expecting them to rely on
memory. If your helper is not an experienced gardener, accept any fatalities or damage with equanimity.
All Hartley Botanic’s Glasshouses and Greenhouses are handmade, bespoke, and made to
order. Customers interested in purchasing a Hartley Botanic Greenhouse should visit
http://www.hartley-botanic.co.uk or call 01457 819 155 for more information.
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