Greenhouse Bulbs – Growing Hyacinths


Greenhouse Bulbs - Growing Hyacinths Bulbs are imported from the Netherlands where their culture is a specialized task, especially when required for forcing. It is of interest to note that the two main methods of hyacinth propagation are cross-cutting and scooping. Cross-cutting involves three cuts over the base of the bulb deep enough to inactivate the main bud, bearing in mind that the hyacinth bulb, in common with all true bulbs, is a flower in embryo surrounded by leaves. Scooping is carried out with a special knife, the object once again being to destroy the main bud, yet cut the base of the scale leaves. After either process, the bulbs are placed in a room where the environment can be controlled to fine limit in respect of both temperature and humidity until young bulbs are formed in the cut section at the base of the bulb. Parent bulbs, complete with these young bulbs, are planted in the autumn, generally in late autumn, when they will eventually develop to the selected size after a process of lifting and replanting.


Bulb preparation

Hyacinth bulbs bought for early flowering have been ‘prepared’, this being a physiological process which affects the development of the flower bud. Bulbs intended for early flowering are lifted in early summer and stored at 30°C (86°F), gradually reduced to 25.6°C (78°F) during a period of 4-5 weeks, and thereafter to between 22.8-20°C (73-68°F) according to variety until the flower is completely developed inside the bulb when the temperature is lowered to 17.2°C (63°F). This treatment varies according to the intended time of flowering. Occasionally there are bad batches of bulbs which fail to flower well.

Bulbs are purchased according to size, from 18-19cm down to 14-15cm, and the price is usually commensurate with size, although in many cases smaller bulbs will flower better than large ones simply because the large flower of top sized bulbs is difficult to support and tricky to handle.

When bulbs come from the supplier they should be unpacked immediately and kept at between 12.8-15.6°C (55-60°F) or preferably cooler, as this will accelerate growth by assisting with the rooting process.


Planting Hyacinth Bulbs

Hyacinths require little in the way of nutrition, as all the strength necessary is already contained in the flowers and scale leaves. Physical condition of the planting medium is, however, important. Sand and peat or peat alone are the usual choices, it being important in both cases to ensure that sufficient lime is added to bring the pH up to above 6. When bowls without drainage are used, peat and lime (shell) plus some charcoal (bulb fibre) is frequently used, a medium which tends to keep sweeter than soil-containing media. Whatever the chosen medium, it should be reasonably moist and should not have been used for bulbs before.

All containers, whether boxes, pots or bowls, should be at least 10-12cm (4-5in) deep. Place the bulbs in with the nose showing when they are to be grown to the flowering stage on benches or pots; leave them half-covered for easier lifting if they are to be potted up in bowls after forcing. Spacing of the bulbs will vary according to whether they are being grown to maturity in pots or boxes or for forcing. Space out if growing to maturity, while for forcing they can be packed fairly tight. They should be firmed in moderately. Some gardeners prefer to plant hyacinths in a double layer so that they will have a solid mass of flowers.

Note that for Christmas flowering, hyacinth bulbs are planted in September; for January flowering in October; up to November for February flowering. When unprepared hyacinth bulbs are grown for still later flowering, planting in October is normal.


Root development

The prime requisites for bulbs after planting are coolness and moisture, during which period they develop sufficient roots to sustain them for flowering. The commercial grower frequently lays out his boxes on a flat surface out of doors and covers them with a thick 5-30cm (10 — 12in) layer of straw which is kept moist, the bulbs being kept cool by the principle of loss of heat on evaporation. On a small scale a good layer of peat, sand or even well-weathered ashes will suffice. Dark cupboards, sheds or cellars may also be used, it being remembered that a cool moist atmosphere of 9-10°C (48-50°F) is the ideal. Occasional watering may be necessary to achieve this.


Forcing hyacinths

Bulbs are brought into warmer tempera- tures when the shoots are about 3.75-5cm (1-½ – 2in) long with the flower bud well through the neck of the bulb. Long shoots result in weak flowers. For the first 10-12 days semi-darkness is desirable, which in a greenhouse will necessitate shading with paper or other material. Shading will induce the flower bud to extend without extensive leaf development. Temperatures of 18.3°C (65°F) initially, raised to 22.8°C (73°F) are ideal; on a small scale much can be done in a heated propagating case to save costs. Excess bottom heat should be avoided and, when benches have heating pipes underneath, a thick layer of peat should be put on the bench to prevent rapid drying out. Bulbs are kept well watered and not exposed to excessive sunlight, but care must be taken not to pour too much water on to the neck of the bulb as this will encourage the development of botrytis. Light spraying helps to keep a humid atmosphere and reduces watering needs. Temperatures should be lowered gradually as flowers begin to open.

For ‘natural’ growing the bulbs are taken out of the ‘plunge’ or dark area and merely given normal greenhouse temperatures, or taken into the home. The same philosophy of shade for a period should, however, be adopted for best results.

Commercially, hyacinth bulbs are lifted when in flower and planted up in decorative bowls.


Forcing in daylight-excluded structures

When bulbs are forced in light-excluded structures they are given temperatures of 23.9°C (75°F) until the flowers begin to open,  dropping to 21.1°C (70°F) until colour is showing and finally to 18.3°C (65°F) to complete the process. The level of lighting necessary is 100W/ m2/ sq yd operated for 12 hours in each 24.


31. March 2011 by Dave Pinkney
Categories: Bulbous Plants, Greenhouse Gardening, Plants & Trees | Tags: , , | Comments Off on Greenhouse Bulbs – Growing Hyacinths


Get every new post delivered to your Inbox

Join other followers: