Greenhouse growing guide
Guide ... Monthly tips from
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 Fl
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 bought from specialist nurseries. Prepare or buy-in
seed and potting cormposts 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 successive sowings of salad crops, including
radishes and beetroots. Also sow vegetables -onions, turnips, parsnips,
etc.- for later transferring to outdoor plots. Sow tomatoes at end of
month. Some early-flowering bulbs may be sufficiently well rooted to
remove from their plunge bed. Sow border plants for the garden -e.g.
delphiniums, Fl 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.
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 over-wintered pot plants
can also be started into growth. Shoots removed during shaping or
training can be used as cuttings 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 blinds or paint-on shading. Ventilate 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 very sunny. Watering will have to be generally increased.
Avoid exposing seedlings to direct sun and make sure they never dry
out. Prick-out seedlings and pot-on promptly. Water-in with Cheshunt
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 begs or 9in pots. Avoid growing in the border
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 supports later. New plants of pelargoniums, fuchsias,
chrysanthemums and perpetual flowering carnations, bought-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 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 temperatures over about 80
degrees F (27C). 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 need dis- budding 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 root in pots under glass.
AUGUST ... Reduce watering
melon plants as the fruits begin to ripen. All kinds of pelargoniums
and many 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 phlox
drummondii, schizanthus, salpiglossis, larkspurs, calendulas, stocks
and any choice, compact garden favourites. It pays to buy the dearer
varieties for pots. Pot on arums, 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 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 then in moist sand
or peat outdoors. Have a general tidy up, cleating 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 clean shading paint off glass. 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 being 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 and service
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 the winter.
NOVEMBER ... From now on
ventilate freely whenever outside temperatures 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 the 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 salad 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 grapevines 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. There should be plenty of
colour from previous sowing 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 degrees F. 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.