Growing and training plants in a greenhouse

Where should I buy my greenhouse plants?

Greenhouse plants should preferably be bought from specialised nurseries—there are many long-established and reliable firms. The same applies to seed. Plants are ideally obtained as young specimens or rooted cuttings, or they are grown from seed. Such plants are usually more vigorous than old mature specimens, which are not only more expensive but can be temperamental after a change of environment. Many greenhouse plants that are commonly raised as house plants are sold at Marks and Spencer stores.

Have you any general advice on sowing and tending seeds?

Buy only the best-quality seed, and sow it as soon as possible. The catalogues of seed firms usually give guidance as to the optimum temperature needed for germination. For tender species and half-hardy plants you may need a propagator. Always use a proper seed compost for sowing, and do not sow deeply; very fine seed should not be covered with compost. Water in by spraying with a fine mist of water, and make sure drying out does not occur at any time after sowing. Cover the sown containers with clean white paper and then with a sheet of transparent glass or plastic: the paper will prevent condensation from waterlogging the seed, and the glass helps the compost to retain its moisture. Always sow thinly to make pricking out easy, and prick out as soon as the seedlings can be safely handled—the sooner the better for minimum root disturbance. After sowing, keep the containers out of direct sunlight but not in the dark. Give the seedlings good light to ensure sturdy growth and avoid excessively high temperatures, which will cause them to become drawn, pale, and weak.

I wish to raise plants from seed. Can many greenhouse plants be grown in this way?

Seed is an exciting source of new plants. Even the ever-popular ‘geranium’ (Pelargonium) can now be grown to produce superb flowering plants in only about three months from F1 hybrid seed. Nearly all the most showy popular pot plants are grown from seed, and many long-term perennials can also be cheaply obtained this way. Some firms specialise in unusual and rare seeds from many parts of the world. Germination of these may sometimes be a gamble, but if you get results it can be a source of great satisfaction.

I have noticed a reference to ‘stopping’ a plant in a gardening magazine. What does this involve?

It means snipping off the growing tip of a shoot or stem in order to halt development at that point and to encourage growth of snoots from below—usually in generous numbers. Thus, when stopped, a plant develops a branching, bushy shape. In a flowering plant each shoot will usually carry flowers and a much more showy effect is obtained by stopping. Many greenhouse and pot plants have to be stopped at some time, often at the seedling stage, to keep them compact and improve their decorative effect or cropping performance. Sometimes the new shoots that form after the first stopping are themselves stopped to develop an even bushier specimen.

What is the point of disbudding?

Some plants develop numerous buds at the end of a flowering shoot. If these are left undisturbed they will eventually become overcrowded and form a tangle of undersized, poor-quality blooms. Disbudding involves removing at the earliest possible stage all but the leading bud(s)—which are usually at the tips of stems and are slightly larger than the others—so that the full resources of the plant can be directed to developing the bud or buds remaining. Typical plants needing to be disbudded are carnations, chrysanthemums, begonias (removal of the female flowers with their winged seed capsules) and camellias (to prevent bud overcrowding).

What are standard plants and how are they grown?

A standard is, essentially, a plant in which a bush growth forms atop a tall, non-branching stem. Standards are usually started early in the year from seed or rooted cuttings and are grown on as a single stem, all side shoots (but not foliage) being removed promptly. When the required height is reached the stem is stopped . This encourages a number of side shoots to form at the stem’s top and these can be further stopped if necessary to form a bushy ‘head’. Then, and only when the head is well formed, can the foliage on the supporting stem be removed. The growing on may take more than a year. If so, in winter, enough warmth must be provided to maintain growth and so prevent dormancy or die-back. If the latter occurs, the roots may survive but the top may die. This means that growth will recommence from the base and the previous work of growing the supporting stem will have been to no avail. Popular plants grown as standards are fuchsias, pelargoniums, heliotropiums, some coleus varieties, datura species, and a number of greenhouse shrubs and marguerites.

How can greenhouse work help to increase my stock of garden plants?

A greenhouse can help you to save a great deal of money because you can raise all your own bedding plants very cheaply in wider variety and often of better quality than if you bought them in shops. Many tender garden plants can be overwintered in the greenhouse, and it is also invaluable for all kinds of propagation jobs. It can be used to raise vegetable seedlings to ensure early crops, and to grow plants for sub-tropical bedding to give the garden a look of distinction. It can also house numerous quite tender plants grown in pots for standing out on patios, window sills, and the like during summer.

How can I best use the space under my staging?

This depends on light conditions. With a glass-to-ground greenhouse, the space will probably be bright enough for a wide range of purposes; it is, for instance, a good place to site a propagator or those plants liking slight shade. If there is considerable shade, as there may be if your greenhouse has base walls, only shade lovers can be put there—but there are lots of these. Many of the most popular house plants like the under-staging area (and may even be raised there); so, too, do many sub-tropical plants and exotic-foliage subjects if warmth and humidity is adequate. Good crops of mushrooms can be grown and, if an area is blacked out, it can be used for blanching and forcing crops such as chicory, rhubarb, and seakale.

The area should not be used to store ‘junk’, which will harbour pests and diseases, but it can be a useful place for keeping tools that are used regularly in the greenhouse and also containers of seed and potting compost as long as these can be effectively sealed.

I have ‘inherited’ a greenhouse, but the only available space for it in my garden is generally shaded. Is it worth the trouble of moving it to my place?

Certainly; the great majority of popular greenhouse and pot plants prefer shady conditions when in the decorative stage—but good light, which does not mean direct sunlight under glass, is essential for them in their early stages of growth. If there is too much gloom, growth will be weak, straggly, and pale. If your greenhouse is going to be very shaded, the use of garden frames in a more open, sunny position might solve the problem of the early growing stages of some plants.

There are also many plants that revel in considerable shade, apart from the low growers suitable for placing under the staging. Examples include many ferns for both cool and warm conditions; Norfolk Island pine (Araucaria excelsa) in its juvenile form; the climbers Chilean bell-flower (Lapageria rosea) and Hoy a camosa—both with attractive flowers; many ivies; the Schefflera foliage species; camellias, which flower very well in pots when young; streptocarpus, gloxinias, and many of the Gesneria family; the ‘forest cacti’ such as schlumbergera and rhipsalidopsis; the annual Exacum affine, which is sweet smelling; Anthurium aystallinum; and various palms. There are many more possibilities to choose from, depending on the temperature maintained.

I would like to grow some plants for winter colour. Any suggestions?

Winter colour is one of the chief delights for the greenhouse gardener. Suitable plants include the following: Cinerarias (Senecio); calceolarias; Primula obconica (many fine varieties) and P. sinensis; numerous hardy bulbs and other storage organs if potted early, such as narcissi (daffodils), hyacinths, and so on; the winter cherry (Solanum capsicastrum) for its scarlet fruits; cyclamen; Erica hiemalis; Christmas cactus (Schlumbergera); Browallia speciosa, including dwarf varieties; chrysanthemums, perpetual-flowering carnations, gerberas, winter-flowering pansies and stocks grown in pots, and the new multi-coloured primroses. A number of shrubby plants, such as camellia (suitable varieties) and various Acacia species, also give good winter colour.

A friend has offered me his small greenhouse free. I have space to spare—but I have one greenhouse already. Apart from extra capacity, what are the advantages of a second greenhouse?

The chief advantage is that you can create two quite different environments—one, perhaps, devoted to a special purpose or to growing plants such as orchids, alpines, carnations, and the like which would not thrive in the sort of environment you create in your present greenhouse.

A second greenhouse would also be useful to keep as a conservatory for the display of decorative plants, and quite separate from the place used for the vital visually less interesting jobs of propagation and growing-on. Bear in mind, however, that even if you have room (or time or the money) for only one greenhouse, you may be able to create at least two different environments by dividing the structure into two compartments.

How can I keep my greenhouse ‘in production’ all the year round?

There is a very large number of possible permutations, and the main thing is to plan well in advance. A typical example of a schedule is to start in spring by sowing bedding plants and planting summer- and autumn-flowering bulbs. Cuttings can be taken of summer- to autumn-flowering pot plants, and crops such as tomatoes, sweet peppers, cucumbers, and melons can be grown. With the approach of autumn, chrysanthemums can be moved in; and the winter can continue to be colourful from sowings of suitable plants made during summer. There is also a number of useful winter salad crops, lettuce being most important.

Can you explain some of the tricks involved in growing plants out of season?

The fact that a greenhouse gives weather protection and generally elevated temperatures is sufficient to give out-of-season results in many cases without resorting to trickery. However, a number of decorative plants do lend themselves to flowering-time control by manipulation of the length of daylight. This can be reduced by blacking-out or extended by using special artificial lights. The procedure is rather complicated and needs experience and expertise, and is more suited to commercial nurseries. A number of bulbous plants can be bought in a specially ‘prepared’ form for early out-of-season forcing, but these may need rather more warmth than is maintained in the average greenhouse.

Can you suggest some shrubs that won’t crowd out my greenhouse?

There are a number of dwarf forms of shrubs that can be grown in 125 mm (5 in) or slightly larger pots. Examples include miniature roses, pomegranate (Punica), lantanas, and Lagerstroemia indica—all of which can be grown from seed. Young camellias flower extremely well in small pots, and there are numerous colourful azaleas (both these are ideal for cold conditions), and several pretty Acacia species. Hydrangeas can be kept fairly compact in pots; and so, with careful management and proper pruning, can many other popular shrubs, including the oleander (Nerium), the calamondin orange (Citrus rnitis), Daphne odora, coral tree (Erythrina crista-galli), Plumbago capensis (which with drastic pruning can be pot-grown instead of being grown as a wall shrub), and Tibouchina semidecandra (syn. T. uruilleana); fuchsias, too, should not be forgotten as shrubby subjects with a long flowering period.

Generally the pruning, shaping, and cutting back to maintain neat, compact development should be done soon after flowering is over.

I thought it might be nice to grow some plants for use as gifts at Christmas. Any ideas?

Special dwarf, compact, and early varieties of cineraria (Senecio) and calceolaria are colourful favourites; of the latter, the new variety ‘Anytime’ is particularly easy. Primula obconica is a fine pot plant, too—but it gives some people a rash if they have sensitive skin. The Christmas cherry (Solarium capsicastrum) has bright red berries, and so have some forms of the red pepper (Capsicum annuum), which are often easier to grow. All these can be raised from seed.

The popular poinsettia, with its colourful bracts, cannot be grown for the Christmas period without special artificial-light treatment. It should be fully enclosed in a thick, black plastic dustbin liner every night (from about 6 pm to 8 am) from late September to late November to give it long nights. Flowering and bract coloration will then be initiated.

Are there any general rules for the over-wintering of plants?

The great enemy of plants when temperatures are low in winter is dampness or over-watering. During very cold spells it is usually best to withhold water entirely (plants that are dormant or resting should in any case be watered only very rarely—perhaps just enough to prevent complete drying out). Plants with fleshy roots, and bulbs, corms, tubers, rhizomes, and other storage organs, must be kept quite dry and frost-free or they will rot. They should be stored in containers of clean, dry sand or peat. The greenhouse atmosphere must also be kept on the dry side, and should be ventilated when the general temperature allows. If you have a heating problem due to an extra-cold spell, you can protect your plants to some extent against frost damage by covering them with dry newspaper on bubble plastic anchored with stones.

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