Growing Fruit trees in a greenhouse in pots
Fruit trees may also be grown in the unheated greenhouse in pots, tubs or boxes. The restriction of the roots induces early fruiting and keeps the trees small, while the glass catches the sun’s warmth, thus forwarding growth slightly, protects the blossom and fruitlets from spring frosts and renders protection from birds as the fruit ripens easier. No artificial heating is necessary; in fact it is inadvisable for apples or pears. Cherries, figs, peaches, and plums can be brought along earlier, if desired, by a little additional warmth.
Pot-grown trees raised for this purpose should be bought—apples, sweet cherries, figs, peaches and nectarines, pears, plums and gages are all available. Start with pots of 25 or 27cm (10 or 11in) diameter or boxes of similar dimensions. Crock well to ensure perfect drainage and then cover the crocks with the first layer of compost, rammed firmly down and deep enough for the tree to ‘stand’ on this with its roots properly spread out and with the top roots just covered. The surface of the soil should be at least 2.5cm (1 in) below the pot’s rim to allow for watering. Work the compost around the roots, little by little, and firm it down as you proceed with a blunt-ended stick.
For potting compost, the following formula is recommended by a nursery where they have grown pot trees for over a century: three parts of good fibrous loam; one part of well-rotted manure, and to this mixture add one liter (quart) jar of walnut-sized lumps of chalk per barrow-load of compost.
The usual system is to sink the pots in a bed of ashes in the open garden during 2 the winter. Thus treated, the pots will be safe from frost and the ashes will discourage the entry of worms. Outdoors, the wood will ripen better and the cold weather will ensure that the trees have a proper resting period.
At the end of January, the pots may be taken into the unheated greenhouse. Ventilate freely during the day in mild weather but shut up early to conserve the sun heat. A Little water will be needed at first—perhaps once in the first week or two and once more in February will be sufficient. In March syringing will help the buds to break and this should be continued until the fruit begins to color. Daily syringing should be resumed after picking, until leaf-fall.
By March more water will be required and this should be given daily attention, testing the pots by tapping. Allow free ventilation when the blossom is open, but avoid draughts. Hand pollination is advisable.
A top-dressing of well-rotted manure should be given when the fruit has all set. Pot trees do not bear very large crops and the fruit will have to be thin, particularly in the first year or two, to prevent over-cropping. Ventilators should be covered with netting to prevent the entry of birds when the fruit begins to ripen.
Each year the pot trees should be repotted in October or November. A little soil is scraped away from the surface and then the pot laid on its side and the tree removed. More soil is then scraped away from the roots and the longest of these are shortened by a third of their length. The tree is then repotted using the same compost formula as before. A larger size pot should only be provided when absolutely essential: probably the original pots will suffice for two or three seasons and then one size larger, only, should be provided. New trees can be purchased to make use of the first set of pots.