Getting the Best from Your Greenhouse
Greenhouses for Work and Play
Whatever may be in flower at the time, the basic smell of growing plants, assailing you as you push open the greenhouse door, is peculiarly satisfying. It sets your nose twitching in appreciation. There may be no heat on — just a little sun and a tang of freshness from an open ventilator. You feel relaxed and can work happily at a bench that doesn’t make you stoop. Tidying plants, removing encroaching(don’t let that wretched little trifoliate oxalis with the yellow flowers take a hold), top-dressing and rearranging pots — these and the more basic tasks of sowing and pricking-out all go forward harmoniously in the greenhouse’s pleasant ambience.
To get the most from a greenhouse, I think you need a clear notion of its primary purpose. Is it to be a workshop or is it to be a special kind of living-room — a conservatory, in fact — where the plants and their appearance in situ are what count ?
In the workshop greenhouse we can overwinter tender plants that will spend their summer months outside. We can bring on plants for house and conservatory ; we can raiseand , grow tomatoes, melons, , aubergines — a nectarine or two (peaches will do outside). Looks will count less than productivity.
The conservatory, which preferably is an extension of a living-room, can be devoted entirely to plants that are at their peak. Permanencies should be handsome evergreens that look smart at every season, as do, for instance, many of the tall-growing. Much of its contents will be made up of plants having a temporary season, and these can be moved in and out accordingly. To this end it is a great advantage to have a service greenhouse nearby. What I’m really saying is that, ideally, you should work towards having two greenhouses, or divide one greenhouse into two sections, one for work and one for ‘play’.
A certain amount of utilitarian ugliness is permissible in your workshop greenhouse, but in the conservatory a beady, vigilant eye will forestall your leaving around hideous equipment such as red plastic watering cans and hoses of virulent green. Appearance counts for everything here. Pots of a dull, neutral-coloured or black surface are far to be preferred to the all-tooprevalent, shiny red-brown kind. Manufacturers always tend to equate bright with beautiful. It is for the customer to set standards.
In whichever kind of greenhouse your plants are growing, their health must be your overriding concern. To have the right atmosphere in which they (and other xerophytes apart) can flourish, the air must be humid, yet not close or stagnant if this can be avoided. This is not too easy to achieve the whole year round. In winter, humidity can be taken for granted ; it will be too high — likely as not — and at low temperatures, destruction of soft-leaved plants by the grey mould fungus, Botrytis cinerea, which mantles them with a sort of grey fur coat, can be very serious.
Prevention is better than cure. Allow a through current of fresh air whenever the weather permits. Don’t water too often. The best way is to let your plants get rather on the dry side before giving them a thorough soaking that will work right through their pots and last them for several days, perhaps a week in certain weathers. Water the potrather than the plant itself, leaving as little water on the foliage as you can and, by the same token, water in the morning for preference, as foliage will then have its best chance of drying off before the night-time period of slowest evaporation. Life will be made easier if some heating is available, but it is surprising what can be achieved by keeping the temperature just above freezing point.
In summer, the problem is to keep the temperature down and the humidity up. It is at this season that I am most conscious of the unhappy atmosphere in many greenhouses — a lifeless, brittle feel. The fact that half their contents have been moved out does not help, because a luxuriance of vegetation means a great area of leafage to hold and give off moisture.
Slatted benches do not retain moisture. Solid benches are preferable by far. If you go in for capillary watering, they will be solid and covered in moist sand anyway, but if you have a varied collection of plants all with different watering requirements, the capillary method may give you insufficient control. In that event, benches covered with a 2.5cm (1 in) layer of grit are more satisfactory.
An earth floor under the benches can be colonized by shade-loving plants which themselves act as a reservoir of moisture in summer. If the whole floor is concreted over it will be harder to keep up the humidity in summer, when you must also allow as much ventilation as possible. The door may be left open for weeks on end. Shading can be arranged with blinds or a sprayed-on wash. This will be obligatory if you are growing large numbers ofor orchids that would otherwise scorch ; smaller numbers can usually be grouped in the shade of taller plants. Given abundant reserves of moisture from water-holding surfaces, whether leafy or of earth or grit, it is possible to do without shading altogether, but if you have trouble from red spider mites turning the foliage of peaches, primulas, daturas and other soft-leaved plants to parchment, it is a sure sign that the atmosphere is insufficiently humid.
And it is the humid atmosphere that imparts that pleasurable greenhouse smell and feel which we noted at the start. Please the plants and we shall please ourselves.