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January 13, 2010
If anyone knows how to make the perfect cedar greenhouse, it's Alton. We believe our current range is the finest yet full of growing benefits! Here is our guide to greenhouse gardening throughout the year designed to help you get the most from your Alton greenhouse:
JANUARY
Sow hardy annuals for growing as pot plants. Most dwarf, compact varieties are suitable. In a warm propagator, sow slow-growing plants like begonias and F1 hybrid geraniums for summer bloom. Gloxinias, streptocarpus, and smithiantha can also be sown in the warmth of a heated propagator. Sow freesias for summer flowers. Sow salad vegetables like lettuce and carrots.
Chrysanthemums and carnations can be propagated from cuttings using small shoots growing from plants saved from last year. New cuttings can be brought from specialist nurseries. Prepare or buy-in seed and potting compost for the busy months ahead.
Pot-on plants like calceolarias, cinerarias, primulas, schizanthus and salpiglossis, being grown for early spring display. Watch out for leaf moulds on these and spray with systemic fungicide if necessary. Ventilate whenever weather permits.
FEBRUARY
Pot lily bulbs and sow seeds. Keep up successful sowings of salad crops, including radishes and beetroots. Also sow vegetables - onions, turnips, parsnips etc - for later transferring to outdoor plots. Sow tomatoes at the end of the month.
Some early-flowering bulbs may be sufficiently well rooted to remove from their plunge bed. So boarder plants for the garden - e.g. delphiniums, F1 hybrid chrysanthemums and sweet peas - these will flower well the same year if given an early start.
Sow flowering greenhouse pot plants like thunbergias, exacum, impatiens, cupheas, and foliage subjects like grevilleas and jacarandas. Also sow solanums for Christmas berries. Bring potted strawberries in from the garden and put in good light for an early crop.
For hardening you plants before planting, an Alton cedar cold frame could prove useful this month, view our Greenhouse Accessories page for more details.
MARCH
Sowing of most bedding plants can be started now, but leave quick-growers like African and French marigolds, zinnias and nemesias, for a few weeks.
Storage organs of gloxinias, begonias, caladiums, achimenes, gloriosas, hippeastrums and other greenhouse bulbs can be started into growth.
Pelargoniums, fuchsias and other overwintered pot plants can also be started into growth. Shoots removed during shaping or training can be used as cutting for propagation.
Greenhouse crops like cucumbers, melons, sweet peppers, aubergines, Cape gooseberries and again tomatoes, can be sown now. So, too, can sub-tropical bedding for summer, such as ricinus and ornamental maize. Start dahlia tubers into growth and take cuttings of new shoots.
APRIL
There should be a great deal in flower now from bulbs and pot plants like calceolarias and cinerarias sown last year.
Keep the temperature down to prolong the display and prevent wilting - the sun will now be quite strong. Shade the glass with internal or external blinds. Ventilation when weather permits, but beware of high winds. Be on the lookout for common pests like aphids and whitefly and keep insecticides at hand for immediate action. Do not use insecticidal smokes if conditions are warm and sunny.
Watering will have to be generally increased. Avoid exposing seedlings to direct sun and make sure the never dry out. Prick-out seedlings and pot-on promptly. Water-in with chestnut compound to prevent damping off. Grapevines growing under glass will be producing new laterals. Tie to wires. Pinch flowering shoots back to two leaves after flower truss.
MAY
Set out tomatoes and cucumbers in growing bags or 9 inch pots. Avoid growing in boarder soil if it hasn't been sterilised.
Attach strings or wires to roof bars to train cucumbers and melons. Tomatoes can be given vertical strings for support. Other crops like sweet peppers, aubergines and cape gooseberries, should also be potted into their final containers and may need support later. New plants of pelargoniums, fuchsias, chrysanthemums and perpetual flowering carnations, brought-in as rooted cuttings earlier, will need potting as roots fill the pots.
Sow all kinds of greenhouse primulas, as well as cinerarias and calceolarias, for display from Christmas onwards. Harden-off bedding plants by standing them outside during the day or placing in cold frames.
JUNE
Greenhouse conditions need careful attention during the summer months. Make sure shading is sufficient. Don't neglect watering. Regularly damp down floor and staging. This reduces water loss from plants by raising the humidity and has a cooling effect as the water evaporates. Maintain good ventilation, tomatoes and cucumbers will be cropping if sown early. Tomatoes will not ripen perfectly in temperature over about 80°F (27°C). Promptly remove all side shoots. Pick off any male flowers (no tiny fruit attached) from cucumbers should they form. Sow sub-tropical and tropical ornamentals or seeds needing moderate warmth for germination. Many of these subjects can be grown-on quite cool after germination. Some large plants can be stood outdoors to give more greenhouse space in summer. Pinch out tips of fuchsia shoots to encourage more stems to carry flowers later.
JULY
Many vigorously flowering or cropping plants will need feeding. Use balanced feeds according to label instructions. Many plants, particularly carnations, need supports. These and begonias also needs dis-building to obtain large blooms.
Keep a watch out for aphids, whitefly, and red spider mite - make sure you look under foliage.
Tap tomato plants and spray the trusses to ensure pollination. A proprietary tomato set spray may sometimes encourage better setting.
Remove faded flowers and seed heads from pot plants to prolong flower production. Pot up lachenalia and nerine bulbs for autumn to winter display. Cucumbers and melons must be kept moist, but on no account overwatered. Take cuttings of shrubs like hydrangeas and roots in pots under glass.
AUGUST
Reduce watering melon plants as the fruits begin to ripen. All kinds of pelargoniums and many kinds of other ornamentals can be propagated from cuttings now. Make sure the stock plants are strong and healthy.
Begin sowing hardy and half-hardy annuals for growing-on over winter. Examples include phiox drummondii schizanthus, salpiglossis, larkspurs, calendulas, stocks, and any choice compact garden favourites. It pays to buy the dearer varieties for pots.
Pot on arums. Pot on calceolarias, cinerarias, primulas and other pot plants sown earlier. Top dress tomatoes and cucumbers to encourage new basal stem roots. Take leaf cuttings of foliage plants like begonias and of ornamentals like saintpaulias and streptocarpus, if they can be kept growing in slight warmth over winter.
SEPTEMBER
The potting of a wide range of hardy bulbs, such as daffodils and hyacinths, can now commence, but leave tulips until next month. Plunge them in moist sand or peat outdoors. Have a general tidy up, clearing out all plants past their best and removing faded flowers and fallen leaves from staging and floor.
Plants that have been standing out during summer may need bringing in where there's risk of early frost. Check for health and presence of pests before doing so. Many perennials and greenhouse climbers that have flowered can be pruned back. Check whether the greenhouse needs any minor repairs or renovations before winter.
Cease damping down and remove shading. Very gradually reduce the amount of water given to tomatoes and cucumbers.
OCTOBER
Clear out the remaining tomato plants that are over and right at the beginning of the month bring in chrysanthemums grown-on in pots outdoors over summer.
Reduce watering plants with storage organs that have finished flowering, dry off and store in frost free conditions, in dry sand, over winter.
Pot tulips and Easter lillies. Sow cyclamen in warmth - if necessary, in a propagator. Inspect heating equipment if necessary. Plastic lining, such as bubble polythene, can be put inside the greenhouse to minimise heat loss over winter. Electric warming cables can be used for economical heating of staging or frames inside the greenhouse.
Shut off any automatic watering equipment and avoid excessive humidity over winter. Bring in chrysanthemum stools and dahlia tubers and store for winter.
NOVEMBER
From now on ventilate freely whenever outside temperature permit to deter grey mould fungus and fumigate with fungicide smokes for the same reason.
Special attention to ventilation is needed with non-flued paraffin and gas heaters. Tap off any condensation that forms on plastic lining to get maximum light and keep all glass sparkling clean over winter months.
Many pot plants, like fuchsias and pelargoniums, should now be rested by keeping on the dry side. Cut out any straggly growth. Sow lettuce and other crops for winter. Some can be gently forced if grown in beds with soil warming cables.
Make sure you have a maximum and minimum thermometer regularly reset to check on minimum temperatures. Plant grape vines in pots, or with the roots outside the greenhouse and shoots trained inside. Dig up rhubarb crowns from the garden and force into growth under the staging.
DECEMBER
Have some form of emergency heating ready, such as a paraffin heater, in case of freak cold spells or main heating breakdowns. These are available from many Alton retailers.
There should be plenty of colour from previous sowings of cinerarias, calceolarias, solanums and primulas for Christmas cheer. Cyclamen sown about 14 months ago should be blooming but must be kept at a steady 50°F (10°C).
For all plants making growth, watering should be cautious and only nicely moist conditions maintained. During longer periods of cold, water very sparingly - if at all.
Some bulbs being forced for Christmas can be given extra warmth, but this may be more convenient in a warm room in the home. Pot specially retarded lily of the valley crowns for flowering pot plants.
Sow more winter salad crops. Note that not all lettuce varieties are suited to greenhouse culture.
Hopefully, by following all this advice, you will have a fantastic growing year in your Alton greenhouse. Good luck & happy greenhouse gardening!
Please let us know how you get on growing in your Alton greenhouse. Please email
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with your stories of success!!
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