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Greenhouse Gardening Guide

Gardening in the Greenhouse

This is a major topic, we are giving you a taster here. There are estimated to be approx 3 million greenhouses in Britain. Tomatoes are a favourite to grow, as is raising seedlings etc. Pests will try to bother you and ventilation is important. Use compost or sterilised alternative, not garden soil. Air that is too dry encourages pests and poor growth, over watering and damp air encourages diseases. Ideally water in the mornings, but evenings is ok in warm weather.

The rewards of seeing something you have tended blooming for many weeks or gracing your dinner table makes greenhouse gardening one of the joys of the gardening world.

Winter Months

We tend to forget our greenhouses in the winter, but when an unexpected mild day tempts you outside, there are jobs to be done.

Check on any plants you are overwintering, removing any dead leaves and flowers, as these are more likely to suffer disease as they die back.

Ensure your greenhouse heater is working, if it’s a paraffin heater check it’s full, and your thermostat is at a satisfactory temperature. Don’t lose the plants you have tended and nurtured because they will succumb to the cold!

Ventilate whenever possible and leave the door open when it is warm. This will help to prevent the fungal problems which thrive on damp, still air.

Now settle down with the seed catalogues and start planning for the New Year!

Autumn Months

First the boring maintenance bit – have an ‘autumn clean’ – brush and sweep out. Wash used pots. Remove dead leaves and flowers to avoid fungal diseases – the greenhouse gardeners’ enemy. You will want as much light as possible over the winter months, so check nothing is causing severe shade outside. Check your greenhouse heater is working, you have paraffin in a suitable safe container, and bubble wrap/fleece in stock. So many parcels arrive swathed in bubble wrap these days that you may not need to buy any – its not horticultural wrap, but will do the job.

Best to take cuttings from your favourite tender perennials as a severe winter could kill them off. Friends will always be glad of any you don’t need next Spring.

Bulbs – the advice is mixed from the experts. Some advise digging them up and keeping them frost free, but others say most will survive if left in the soil – better with a mulch applied – so don’t crowd up your greenhouse unnecessarily.

Tubers – dahlias etc - if you live in an area with cold winters or heavy soil – cut to just above ground level and lift. Dispose of any which show signs of damage or disease. Shake off soil, and stand them upside down for 2 weeks. Store loosely wrapped in your greenhouse. If you have had problems with them rotting use proprietary sulphur made for this purpose.

Plants in containers - if they are too big to move into your greenhouse raise the pots off the ground (pot feet are ideal) and wrap the plant/pot in bubble wrap. Keep sheltered from heavy rain, as your plants can rot. If you have room in your greenhouse you may be rewarded with earlier flowers.

Gladioli corms are happy to be left in the soil – again the magic word – mulch. If you have a prize variety you should follow the growers instructions.

Begonias – not happy winter plants will fare much better if the tubers are lifted. Remove any scabs, and rot and ensure tubers are dry. Store in newspaper. Replant them in your greenhouse in early Spring, avoiding external late frosts.

Mediterranean & Exotic plants. The further North you live, the bigger your problem. If possible bring your plants into your greenhouse before the first frosts. Those you have to leave outside need protection – check on the variety you have for the method most suited to that plant.

Herbs.  Those that need taking into your greenhouse or putting on kitchen window sill if you have the space includes tarragon, oregano, and  parsley.  Basil and coriander are very tender – easier to discard and buy fresh next spring. Parsley will keep growing through the winter and with luck you will be able to continue picking it. Mint, sage rosemary and thyme can be left outdoors and with luck (and a fleece cover) will survive.

It isn’t practical to lift all your beloved plants to overwinter in your greenhouse. We all lost countless hebe and lavender amongst others in the recent severe Winters. Covering with fleece may help, but sometimes we just have to accept the inevitable and buy fresh stocks the following spring. At least you then have a chance to try new varieties.

If you grow sweet peas you may get earlier flowers by sowing them now and keeping in greenhouse or cold frame.

Spring Months

Early Spring is an important time in the greenhouse as many popular flowers are too tender to be grown outside at this stage. Sow your seeds in March or April – remembering to label them and keep the seed packet  for instructions, you wont remember which is which!  They can be moved outdoors in late Spring – late May is ideal when chances of frost have past.

Sow your vegetables which aren’t hardy – cucumbers, tomato, aubergine, peppers etc.  Hardy plants can also be started off in the greenhouse – you should get earlier blooms or crops this way.

Ensure your pots and seed trays have drainage holes, and are clean. Choose compost advertised as suitable for cuttings and seeds. Do not overwater – think damp, not soaked. Follow the instructions given by plant suppliers and look forward to when you can prick them out. Handle carefully – by the leaves is the normal rule, and set approx 4mm apart. Let them rest for a few days, then start to harden them off gradually. This is important. Increase the ventilation or move them to a cold frame. Don’t rush this process – it can be a shock for your plants. Finally leave them outdoors for a few days then plant. Your minimal investment should reward you with masses of colour, and more importantly – satisfaction at your achievement.

Cuttings. You can’t guess when to do it or where to take the cutting from, but here is some general guidance. Plant your cutting quickly after separating it from the main plant, and ensure the compost is covering it. Don’t be tempted to keep scraping the compost away to check if it has taken – just watch for signs of new growth. Remember to use rooting powder.

Softwood cuttings are green – many are hardy perennials and a few small shrubs. Basal cuttings are shoots at the base of the plant and pulled away.

Make a hole in your compost (a pencil does this easily). If it is a large leafed plant reduce foliage by 50%. Firm your cuttings into pots and water sparingly.

Now they need light and some warmth.

Summer Months to Early Autumn

Cuttings - Semi ripe cuttings are green at the top and partly woody at the base - they are usually side shoots with a ‘heel’ attached. Many shrubs and climbers are propagated by this method- follow guidance as for Spring.

Planting out

Watch the growth in your seed trays. Good signs are moist soil, and compact sturdy plants. Don’t leave them so long that the plants have come into flower (where have you been?) or the roots are growing through the tray base.

Water the plants before you lift them to preserve as much soil as possible around the roots.  The soil ball is important, try not to damage the roots.

Ideally pick a day when the garden soil is moist but not waterlogged. If necessary, mix peat into the planting hole if the soil is too wet.  Handle by the soil ball if possible, not the delicate stem. Firm in gently with your fingers or suitable blunt tool.  Plant at the right depth – the top of the soil ball should be just below ground level. Remember to check planting distances required – your tiny seedling will soon become a flourishing plant, so don’t overcrowd at this stage. Again label- until they are established you don’t want a family member pulling out your ‘weeds’!

We hope this has been of interest to you – experiment with plants in your greenhouse – some will fail, but many others will reward you for months in your garden.

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