Guide to Growing Bulbs in the Greenhouse

To the modern amateur gardener the greenhouse, home, and garden are no longer separate entities but complementary units. A popular feature of many houses nowadays is the garden room, in which plants play a vital part in the decorative scheme. The greenhouse serves as a supply unit for both garden and house. Not only does it enable the gardener to work in comfort whatever the weather, but it greatly extends the scope of the garden and also prolongs the flowering season.

Although the temperature of a greenhouse may be cold (that is, unheated), cool, intermediate or very warm, a cool greenhouse is the most practical and economical for the amateur. Most bulbous plants will thrive under cool conditions, in which the temperature is maintained between a minimum of 7°C. in winter and 12 to 18°C. in spring and summer.

Heat for the small greenhouse can be provided in a number of ways. Electric heating, though most efficient and easily controlled, can be very expensive to run. Open coal-gas heaters cannot be safely used within the house because the fumes are toxic, but natural (North Sea) gas gives off carbon dioxide which is beneficial to plants. It is now possible to purchase a natural gas heater which is quite safe. Paraffin heating is probably the cheapest method of all, but care must be taken to ensure that the apparatus is kept scrupulously clean, as again, the fumes can cause damage to plants.

It should be remembered, however, that although some artificial heat will be required to maintain minimum temperatures during the winter months, too much at a time when the hours of daylight are short can be disastrous. In the cool house use can be made of sun heat by putting down blinds or shades at night to cut down loss of heat through the glass, provided they are removed promptly to make full use of all available daylight.

The chief difficulty in a small house is to keep the temperatures down in summer, and the ventilators and shades should be operated carefully to avoid big fluctuations or rapid changes of temperature. It may be desirable to use some artificial heat at night when warm, sunny days are followed by cold, sharp nights involving a sudden drop of temperature in the evening.

Ventilators should also be used to control the atmospheric moisture. In a hot, dry spell, humidity must be maintained by damping down floors and staging and spraying the plants themselves frequently. Shading will also be necessary to protect the leaves from the burning rays of the sun and prevent scorching.

When watering the plants, sufficient water should be given at a time to moisten all the soil in the pot. This is best done by watering directly from the spout of the can and not through a rose, a method which also avoids splashing the foliage. It is important to keep the crown of the bulb dry. Experience will soon show when water is required; it can be judged by the weight of the pot or by scratching the surface of the soil with a finger or, in the case of clay pots, by tapping the side to see if it sounds hollow. A more sophisticated watering device is the capillary bench in which the base material of sand or gravel on top of the bench is kept permanently moist and plants receive water through capillary action.

Daffodils may be planted in a double layer which makes for a very attractive display. The bottom of a large bowl should be covered with a layer of compost. Bulbs are evenly spaced on top of this and covered up to their noses in compost. More bulbs are then placed between the noses of the bulbs in the lower layer and covered with compost so that their noses are just showing It is essential to make sure that all pots are thoroughly clean. The drainage holes must be clear, and crocks should be placed at the bottom of clay pots to assist drainage. This is not essential with plastic pots and pans as the drainage holes are usually adequate. The pot should not be too big for the size of the bulb, or the soil will become sour.

For bulbs planted in pots or pans in the greenhouse, John Innes Potting Compost is a good planting medium, or one of the soilless composts. Other composts are recommended in the descriptive lists. If the bulbs are to be brought into the home for flowering, an ornamental bowl without drainage holes may be preferred, in which case it will be necessary to use special bulb fibre which contains crushed oyster shell and a little charcoal to keep it sweet.

When planting bulbs, the bottom of the pot or bowl is filled with compost or bulb fibre which has been thoroughly moistened. This should be pressed down firmly but not so hard that it will become compacted. The bulbs are laid on the surface of the fibre and when using more than one bulb per pot they should be evenly spaced so that they are not touching one another. The pot is then filled in with compost.

Bulbs can be started into growth either by the method described on Winter Flowering Bulbs for Colour Indoors or more usually they can be stood in a cool, dark place such as a cellar or shed, or under the staging in the greenhouse, the object being to encourage them to form a good root system before too much top growth has been made.

Tall plants such as lilies, narcissi and tulips will need staking, and so will those with delicate stems such as freesias.. Thin green stakes are best since they are the least obtrusive, and the blooms can be supported by cross-threaded strands of cotton.

All bulbs require a resting period after the foliage dies down, but their individual requirements vary. Instructions are given in the descriptive list that follows.

If good standards of hygiene are maintained in the greenhouse, pests and diseases will be kept to the minimum. A constant watch should be kept and spraying with a good derris-based insecticide carried out when necessary against pests such as aphids. When planting, it is important to examine bulbs carefully and discard those that are damaged or show signs of disease. Infested or infected bulbs should always be burned.

Most cool greenhouse owners follow a three-part programme, the main flowering seasons being spring, summer and autumn. This does not mean a flowerless winter, only that less colour can be expected in the depth of winter.

Many of the smaller bulbs are ideal for growing in the alpine house or cold greenhouse in pans or wide-topped pots. This will lead to a colourful display from January onwards. Not only will such protection encourage earlier, cleaner flowers, but they will be seen from a better and closer angle than when viewed in their normal open-ground positions.

Free ventilation is needed to encourage sturdy growth and to stave off mildew. Practically all bulbs can be grown satisfactorily in the John Innes Potting mixtures using well-crocked pans or pots. Watering needs to be carried out with care and particularly in very cold weather it is best to keep the bulbs on the dry side.

The following plants are very suitable for pans or pots in the alpine house: Anemone blanda, crocus species, colchicums, hardy cyclamens, galanthus or snowdrops, Iris reticua/ta, danfordiae, dwarf narcissi, scillas, and tulip species.

08. July 2011 by admin
Categories: Bulbs, Greenhouse Gardening | Tags: , , | Comments Off on Guide to Growing Bulbs in the Greenhouse


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