Early spring in greenhouse
Some tender crops, like tomatoes, peppers and cucumbers, can be sown now under glass, in pots or trays, but kept in a warm, heated propagator for germination and then they will be planted outside in early summer. Also celery, celeriac and squashes can be raised under glass before planting out later.
Many varieties of half-hardy summer bedding plants can be sown now in heated propagators, in a greenhouse. If you have already seedlings from earlier sowings, now is time to prick and space them out in large seed trays or plant them individually into small pots.
You can continue take cuttings of about 5 cm long from new shoots that are developing on overwintered chrysanthemums, and root them in pots of composts in a heated propagator at 13 Celsius degrees (55 F).
Repot large plants of cacti and succulents during spring in very gritty, loam-based compost, preferably in terracotta pots.
Instead of using cold water form the mains, you can always leave a full can of water in the greenhouse to take the chill of it before you will use it. Never overwater the seedlings and when the seeds have germinated remove the propagator lids to improve germination. Damp down the floor of the greenhouse in the mornings of warmer days to increase humidity but open the doors and vents to prevent temperatures rising too much and close them again in the evening.
If you plan to sow a lot, buy in supplies of pots and compost for your early sowing and potting and store the compost bags in the greenhouse so it is already warm for seed sowing.
Mid spring in greenhouse
As days go warmer, you can move young plants from greenhouses into cold frames to get them used gradually to cooler outside conditions, before you will plant them out. Start putting up shading blinds and screens or apply shade paint to protect the plants from the hot days temperatures. On hot days the atmosphere in the greenhouse can become very dry so you can splash water on the floor to increase the humidity.
Open the vents every morning and close them back in the evening, and if late frosts are forecast provide some extra protection for your plants. Keep pricking out seedlings as soon as they are large enough and continue to take cuttings from new growth of dahlias, fuchsias and some indoor plants like saintpaulia and begonia. Repot overgrown plants but make sure to use the same type of compost as before. Sow seeds of primulas as they can be grown as pot plants also.
Late spring in greenhouse
As days are getting warmer a regular damp down in the greenhouse is necessary. Splash water on the floor and under staging 2-3 times a day, to increase humidity levels. Try avoiding great temperatures fluctuations in your greenhouse by using shades. Open doors and ventilators each morning and close them back in the evening and don't hesitate to use the heaters on cold nights.
Check all the plants regularly for signs of pests and diseases, because as the weather gets warmer they start to show up.
You can now pot up begonias and gloxinias tubers, individually into 15 cm pots. Take cuttings of non-flowering shots of new growth of hydrangeas. Also you can now propagate your alpines from cuttings. Keep potting on young plants and rooted cuttings into larger sized pots as their roots grow.
You can also grow some of your crops under glass, using growing bags. Tomatoes, cucumbers, peppers and aubergines are some of the crops that suit to be grown in growing bags. Now is time to plant young plants into growing bags or in soil in the greenhouse border. Feed them with high-potash fertilizer every week from now on for good crops.
Early summer in greenhouse
As the weather is now warm and the sun is strong you need to open the greenhouse doors and vent each morning and to shade the windows by painting or using blinds, in order to keep the temperatures down.
Damp down regularly by splashing or spraying water around the greenhouse to keep the atmosphere moist.
Pot on cuttings that you have been taken earlier from potted hydrangea. Take cutting from coleus, African violets, fancy-leaf begonias, fuchsias, regal pelargoniums, pinks and other house plants, using non-flowering shoots of about 10 cm long.
Keep feeding at least once a week the plants in pots and growing bags, using a liquid fertilizer to make sure the plants are not going short of nutrients in this strong growing period.
Crops that are growing under glass, like tomatoes, peppers or aubergines, need to be watered regularly and fed with high-potash fertilizer every week to help the fruits to develop well.
Mid summer in greenhouse
As this is the hottest period of the year, ventilation in the greenhouse is a must. Open doors and vents daily or just let them open all the time to prevent high temperatures. Re-apply shading paint to also avoid high temperatures inside the greenhouse.
Damp down paths regularly with water to help reducing the temperature, or mist lightly over the plants to increase humidity.
If you have crops under glass, check watering daily, feed them every week and harvest fruits regularly.
Examine plants each week for signs of pests so you can pick them off or treat as soon as possible if any are found.
Keep taking cuttings, as this is the most valuable period when almost anything will root easily from cuttings. Prick out seedlings of plants that you have sown earlier and repot cuttings have have rooted by now.
Late summer in greenhouse
If the weather is still hot, ventilate daily to keep temperatures down by opening doors in addition to roof and side vents. At the end of season nights might become cool so close the vents over the night and remove shadings as days are getting shorter.
During dry, hot days, damp down regularly to cool the atmosphere by water evaporation.
If you have crops grown in bags or pots in your greenhouse, keep them well watered and make sure to never let their compost to dry and feed them regularly.
Keep taking cuttings from tender perennials, pot bulbs for flowers at Christmas, start cyclamens, freesias and lachenalias into growth. Reduce watering of gloxinias when they flowers have finished and once their foliage had dried, pick of and store tubers for the winter.
Check the heaters to see if they are working properly even if the winter seem to be far away, so you will have enough time to fix them if any problem occur.
Early autumn in greenhouse
Begin to reduce watering and stop damping down, continue to ventilate on warm days. Water in the mornings, so plants are not left wet over night - damp, cool air encourages the spread of fungal diseases.
Reduce shading by removing mesh netting, and on fine days take everything out of the greenhouse and wash down the inside with warm water and special greenhouse disinfectant, clearing the glass and staging thoroughly.
Put up insulation such as bubble plastic over the inner roof and walls. Check the heaters to make sure they are on working condition and be aware of night time temperature drops.
Take cuttings from bedding plants and tender perennials. Bring half-hardy plants that have spent summer outdoor, back inside. Remove tomato plants and growing bags to the compost heap.
Pot on spring flowering plants. Begin to take hardwood cuttings.
Mid autumn in greenhouse
Reduce watering now to suit the demands of each pant. It is far better to water individual pots in saucer than to use self-watering benches of capillary matting. Keep the atmosphere as dry as possible. Bring pots of tender bulbs and perennials into the greenhouse for the winter. Many bulbs die down completely, so require no water over winter.
Keep the greenhouse well ventilated and check watering every day. Remove old crops and growing bags once picking diminish. Finish potting on rooted cuttings and seedlings. Get ready to clean glass and fix up bubble insulation. Check that heaters are working efficiently.
There are also few things that you can do to reduce the cost of greenhouse heating. Line the inside with bubble polythene to double glaze it and reduce heat loss. Hang a curtain of polythene across the doorway. Use thick sheets of white polystyrene to line the north side, especially under the staging. Mend poorly fitting doors and vents, sealing over low-level vents completely with clear polythene. Replace cracked panes. Place dustbins filled with water under greenhouse staging to act as storage heaters. These warm up during the day, releasing their heat at night. This warm water can also be used for watering plants.
Late autumn in greenhouse
Growing conditions are now much cooler and damper so the proper way to water now is just sparingly. Try not to wet plant leaves. The compost of some plants, like pelargoniums, can be allowed to dry out almost completely for the winter. You can now sow lettuce for early cropping.
Check heaters daily and use a max-min thermometer to make sure that the temperatures are not set to high, wasting heat. Make sure also that the greenhouse is well insulated, but ventilate freely on days that are still warm.
Small collections of tender plants and rooted cuttings can be over-wintered in a heated propagator. These are far cheaper to run than heating an entire greenhouse.
Greenhouse pests can cause problems as the heat and protection in a greenhouse makes conditions ideal. Good hygiene is essential in controlling pests, removing dead leaves and plants and cleaning away the debris that pests can hide in. Water plants in the morning so they are not left wet overnight - damp, cool air encourage the spread of fungal diseases.
Early winter in greenhouse
Check pelargoniums, fuchsias, argyranthemums and any other overwintering plants, removing any dead or yellowing leaves. Cut down the tops of pot-grown late-flowering chrysanthemums to their base. Store in a greenhouse or cold frame.
Insulate greenhouse with bubble polythene or other materials. Check heaters daily to make sure that they are working efficiently. Monitor, using a max-min thermometer, to avoid big temperature differences. Clean empty greenhouses scrubbing down the frame and staging and cleaning the glass inside and out.
Sow onion seed in pots or trays in the greenhouse for the biggest crops. Remove all dead and diseased or damaged plants, leaves and debris.
Mid winter in greenhouse
If you want to have early nice lilies now is time to plant them in patio pots and keep them in the greenhouse to develop. Sow seeds of slow-maturing half-hardy summer bedding plants like verbenas, pelargoniums and begonias in heated propagators.
Take cuttings from greenhouse chrysanthemums, prune greenhouse wines while completely dormant and clean off dry bark from their rods. Winter prune climbers like passiflora and bougainvillea.
Bring tender shrubs, like camellias, that are grown in containers, into a cold greenhouse for extra protection. During cold weather water your greenhouse plants only sparingly. Check the heaters regularly to see if they are in good working condition and that fuel levels are high enough to last the night.
In warmer days give your greenhouse a thorough clean, washing the glass inside and out and scrubbing the framework and staging with disinfectant to remove dirt and overwintering pests.
Late winter in greenhouse
In this period, you greenhouse still need a good insulation, so make sure it is well insulated with bubble polythene and the heaters are working well.
For an early flowering and fruiting start of the strawberries now is time to bring pot-grown plants into the greenhouse to encourage them to vegetate. Continue to sow seeds of summer bedding plants in heated propagators, like begonias, pelargoniums, nicotiania, petunia or salvia.
If you already have seedlings, prick them out and space in larger trays so they will have enough room to develop, as soon as they are large enough to handle by their new leaves. Avoid keeping too wet the seedlings as the warm and moist conditions in a warm greenhouse will cause the rotting of the young seedlings.
You can even plant some bulbs, corms and tubers in a heated greenhouse now, like dahlias for encourage them to develop new shoots and use them for cuttings, or begonias, gloxinias and achimenes for an early display.
You can now prune back hard your fuchsias, to the base, to leave a well shaped plant and you will see that new shoots will soon develop in a warm greenhouse. You can also use this pruning for take cuttings for new plants. Tips of 2.5 cm shoots will root successfully in a heated propagator in a mixture of equal parts of peat-free compost and vermiculite.
