Give your greenhouse a sunny outlook

By Hannah Stephenson

While many gardeners wait until autumn to carry out vital greenhouse maintenance, summer is also a good time as it's generally warm enough for you to put pots outside to allow you to move around inside.

Greenhouse and frame maintenance should be carried out a couple of times a year, ideally in early spring when you can clean the glass inside and out, wash down the staging and remove debris from guttering.

At this time of year, take advantage on dry days by making sure the glass fits snugly to the frame and replace any broken panes, wearing gloves and a pair of goggles.

Use a hose and long-handled, soft-bristled brush to clean the roof glass, while you can take a washing-up cloth to the sides going over all areas, because even if the glass looks clean, it will probably have a thin layer of algae on it. Where panes overlap, use a lolly stick or plastic plant label to ease out the dirt before giving the area a squirt with the hose pipe.

Clean out debris from guttering and check that the brackets are sound and firmly attached and that there are no leaks. A leaking gutter is a common cause of rotting frames in wooden greenhouses. Small leaks can be repaired with a flexible, transparent, silicone polymer applied with a mastic gun, but for larger leaks, you may have to fit new gutters and downpipes.

Wooden frames need to be scrubbed clean with detergent and should be checked for rot. Cut back rotten wood to where it is sound and replace it with naturally durable wood such as pressure-treated timber. New bare wood should be treated with wood preservative. Aluminium frames should only require a quick brush over.

Once you have cleaned the outside, bring your plants outdoors if weather permits and remove weeds from the corners of the greenhouse and gaps between the paving stones of the path. Wash and clean the glass and frame inside, sweep away debris and wash down staging, which will help prevent problems from pests and diseases over the winter.

The resting stages of pests, especially the non-feeding adult females of red spider mites, can be hit hard by washing down. Allow the greenhouse to dry before moving the plants back in and check vents, lubricate hinges and adjust automatic vent openers.

Remember that all the usual greenhouse pests will remain active and breed rapidly in warm weather. Biological controls are very effective in the greenhouse, but be careful not to destroy them with insecticides.

It's wise to give each plant a health check before you bring it back in, weeding it and trimming if necessary. Dead leaves can be removed and you can boost your plant with a new top dressing. Pick off any slugs, snails or other pest and leave any plant which is infested with pests outside for more treatment.

If you have recurring problems with moss and algae on internal greenhouse surfaces, try increasing ventilation. Be aware, too, that algae, moss and liverwort growth can also occur if pots and seed trays are not thoroughly cleaned and sterilised before use.

Best of the bunch - Helenium

These bright perennials with the daisy-like flowers are ideal for pepping up a border when other summer scorchers are past their best.

The flowers, in shades varying from zingy yellow to burnt orange, face towards the sun and bear a prominent central disc. They're ideal for the front or the middle of borders, as heights vary from 60-150cm (24-60in). The taller ones may need propping with twiggy sticks, but the dwarf ones may not need any stakes.

They make great plant partners for bold foliage plants such as white-flowered hostas, ornamental grasses such as Miscanthus sinensis 'Silver Feather', or bergenias.

Heleniums do best in rich, fertile soil and are well suited to wet, sticky clay gardens. If you have poor, dry ground, you'll need to improve the soil, feeding, watering and mulching if they are to survive. Deadhead them regularly to keep new flowers coming.

My favourite is h. 'Moerheim Beauty', a long-lasting burnt orange variety which flowers consistently from August through to September and which does well from lifting and dividing every few years, in autumn or spring. Other top performers include 'The Bishop', which has yellow flowers with a brown centre, and 'Butterpat', an all-yellow flower.

Good enough to eat - Spinach for winter

You may be enjoying your summer harvest, but if you sow spinach now, you'll be enjoying tender leaves in the winter.

Spinach has become a hugely popular addition to summer salads, but it is also delicious wilted in stir fries and pasta dishes or used as a comfort food when creamed and served as a winter accompaniment to meat dishes.

While it is vulnerable to slugs, it's a tough little leaf which can survive harsh frosts and lashings of winter rain.

Sow seeds in modules, thinning to two or three plants per module. Once they are large enough, plant them outdoors in rich, fertile soil containing plenty of nitrogen and cover with netting to protect them from birds. You should be eating new leaves around eight weeks after planting.

Try 'Mediana', a useful all-round variety for sowing in spring or summer to produce baby leaves, or in autumn to grow under cover for cutting the following spring.

Many varieties will overwinter, including 'Early Prickly Seed' which will regrow after a harsh winter, and 'Bordeaux', with bright red leaf stalks which can be sown from July to September.

Three ways to - Tackle clematis wilt

1. Plant your clematis deeply, in moist but well-drained soil.

2. If your clematis has wilt, prune it back promptly to unaffected tissue and destroy all traces of diseased material. Healthy buds may develop from ground level or even below.

3. If you are planting your clematis against a wall, make sure the border by the wall is not too hot and shallow, or improve conditions with organic matter and mulching.

What to do this week

:: Take stem cuttings of plants that do not divide easily, such as penstemons and osteospermums.

:: Continue to layer border carnations and check the progress of those layered last month.

:: Pinch out the growing tips of wallflowers to encourage the production of sideshoots.

:: Remove some of the foliage of tomato plants to give the fruits optimum light levels and the chance to ripen.

:: Give topiary plants a trim to keep them in shape.

:: Prune espalier and cordon-grown apple and pear trees to allow more light and air to reach the tree and improve fruit quality.

:: Harvest the remaining cane fruit, then cut out at ground level all canes that have finished fruiting, removing pests and diseases and allowing new canes to ripen properly.

:: Deadhead summer annuals and remove any seedpods from fuchsias, otherwise the energy of the plant will be diverted into reproduction and it will stop flowering.

:: Sow parsley and chervil under glass in large pots for winter use inside.

:: Collect and dry seeds of dill, fennel and chives as they ripen. They can be resown immediately in seed drills 5-10mm deep, if required to expand the stock in the herb garden.

:: Take cuttings from dianthus, achilleas, dwarf phlox and saxifrages for the rock garden.

:: If you are going on holiday, pick all your runner beans, even the smallest, before you go, to encourage a continuing crop on your return