PRODUCING GRAPE HYACINTHS (as pot plants)

practical tips for

• arriving at a well-considered choice of cultivar, bulb size and pot size
• treating the bulbs properly before the production process
• providing the right horticultural practices to yield a compact plant for pot production
• preventing problems throughout the production phase

 

Choice of right variety and proper planning are important

Varieties for producing pot plants
Muscari armeniacum and its cultivars are most often used for producing grape hyacinths as pot plants. In recent years, however, certain cultivars of Muscari aucheri (‘Blue Magic’, ‘Ocean Magic’ and ‘White Magic’) have become available. The advantage offered by these ‘Magic’ grape hyacinths is shorter leaves.

Scheduling the flowering period
Muscari armeniacum can be forced into bloom from January through April. After lifting and drying, the bulbs are stored at 20°C, the temperature at which flower initiation occurs most quickly. For late-season flowering (March/April) the bulbs should be stored at 17°C from 1 October. A cold period lasting 15 to 16 weeks is necessary for proper flower production. Do not start the cold period before the end of August. Compared with other bulbous plants, flower initiation in grape hyacinths occurs a little later in the season. Starting the cold period too soon will prevent all the individual flowers in the inflorescence from being initiated. For forcing purposes, this will result in inflorescences with a white top and desiccated flowers. The earliest bloom requires 16 weeks of cold to produce good flowering results without flower desiccation. Bulbs intended for flowering in February can be held a week less in cold storage and still produce good flowering results quickly. Store the bulbs under dry, ventilated conditions. If the RH is too high, fungal growth (Penicillium, etc.) can appear on the bulbs. In the early stages, the symptoms will only result in a less attractive bulb. Eventually, however, the fungus can damage the bulb enough to keep it from growing properly.

Prevent tall leaves by lowering cold treatment temperature or planting later

Using cold treatment to prevent tall leaves: should bulbs be stored dry or planted?
An important point to consider when forcing Muscari armeniacum is its leaf development. In some cases, the leaves can grow taller than the flowers, thus making the pots look unattractive. When the bulbs are planted before they go into cold treatment and spend this entire time in a planted state, their leaves will grow too tall. There are two ways to prevent excessively tall leaves. A commonly used method is to leave the bulbs unplanted and maintain a constant temperature of 9°C during the cold treatment until 4 to 6 weeks before housing. At that point, plant the bulbs and continue the remaining cold treatment at 9°C to allow the bulbs to root. Another method is to lower the temperature of the cold period in steps: start the cold period at 9°C for the first 4 to 5 weeks; then lower it to 5°C and even to 1-2°C later. This procedure will retard leaf development. Do not, however, subject the bulbs to 2 to 5°C throughout the cold period because this will result in a very long housing period and tall leaves. Some companies, however, leave the bulbs unplanted throughout the entire cold period. After planting, the pots are put into the greenhouse but are kept there at a temperature not exceeding 10°C. Should the greenhouse temperature be too high, the leaves can emerge before the roots develop, thus resulting in desiccated flower buds. The major advantage of forcing grape hyacinths at a cooler temperature is that the leaves remain short and spread out quickly to reveal the flower bud at the centre of the plant. This produces a visually attractive product, but forcing at this low greenhouse temperature will of course also increase the number of days spent in the greenhouse.
 

Proper care for the highest quality

Coordinating bulb size and planting density
Various bulb sizes are available for forcing purposes: 6/7, 7/8, 8/9, 9/10 and 10/+ cm. in circumference. For Muscari armeniacum, sizes 6/7 and 7/8 will usually produce one flower stem/bulb. Size 8/9 will produce an average of 1.5 to 2 flower stems/bulb, and sizes 9/10 and 10/+ will produce 2 to 3 flowers. Table 3 provides an indication of the number of bulbs/pot.

Number of greenhouse days
The two important factors determining the number of greenhouse days are the temperature and the degree of maturity at which the pots will be sold. If the grape hyacinths are to be sold as sprouted bulbs, they sometimes require only a few days in the greenhouse at 18°C. The other extreme is waiting until the buds start to display colour; in this case the pots will be housed in a cold greenhouse (10-12°C). Depending on the season, this can take 3 to 5 weeks (see Table 2).
Table 2. Cold treatment (both duration and temperatures) for each flowering period. The length of the housing period is based on a greenhouse temperature of 9°C.

bloom date	cold treatment	start of cold treatment	housing period at 18°c
January	16 wks. 9°C or 5 wks. 9°C + 11 wks. 5°C	Mid-August to mid-September	5 weeks
February	15 wks. 9°C or 4 wks. 9°C + 10 wks. 5°C	2nd half of September to mid-October	4 weeks
March	15 wks. 9°C or 4 wks. 9°C + 10 wks. 5°C	2nd half of October to mid-November	3.5 weeks
April	15 wks. 9°C or 4 wks. 9°C + 10 wks. 5°C	December	3 weeks

As mentioned under ‘Varieties for producing pot plants’, the leaves of Muscari aucheri (the ‘Magic’ cultivars) are genetically shorter than those of Muscari armeniacum. The cultivars of this species are usually potted up a few weeks earlier without having to be concerned about tall leaves.
 

Plant carefully and monitor moisture level
Grape hyacinths sold as pot plants are usually planted with their noses just above the soil surface so that consumers can see that they are bulb plants. This also ensures additional ornamental value. Make sure, however, that no more than 1/3 of the bulb is exposed. Leaving too much of the bulb above the soil surface can result in uneven rooting rates that will then lead to uneven crop development. Watering the bulbs thoroughly or immersing them before planting stimulates even rooting and prevents uneven crop development.
Table 3. Number of bulbs/pot.

bulb size	pot size
	9 cm	10 cm	12 cm	16 cm
10/+	4	5	6	12
9/10	5	6	8	15
8/9	6-7	7-8	9-10	17
7/8	7	8	10	20
6/7	8	9	11	21

 
Provide sufficient light and water with care
Once housed, water the bulbs once but thoroughly and then keep the soil moist but not too wet. Wet soil increases the risk of Pythium, a soil-borne fungus. A drier soil will produce beautiful short dense plants. Not providing enough water, however, will produce a very uneven crop. If the bulbs are sufficiently rooted when brought into the greenhouse, a temperature of 18°C is best. If the bulbs are not yet sufficiently rooted, the greenhouse temperature should be kept a few degrees lower to prevent flower desiccation. Provide high light intensities in the greenhouse to promote flowers with good colour. A greenhouse that provides insufficient light will result in light blue flowers. Make sure that the soil in the pots is sufficiently moist so that the plants will have enough moisture during the marketing and distribution phase.
 
 
A publication of: International Flower Bulb Centre P.O. Box 172 | 2180 AD Hillegom | The Netherlands t +31(0)252 62 89 60 | f +31(0)252 62 89 70 info@bulbsonline.org | www.bulbsonline.org Disclaimer The International Flower Bulb Centre accepts no responsibility for any adverse consequences resulting from the use of information obtained from this publication.