If you love the distinct strong fragrance of hyacinths (Hyacinthus), you don’t have to wait for them to poke their heads out in the spring. Hyacinths are especially suitable candidates for forcing indoors, or bringing on an early bloom. This requires a little planning. In order to bloom, the bulbs need chilling for three to four months in a dark, cold environment. Other than that, growing hyacinths indoors is not difficult.
Timing of Hyacinth Chilling
Buying pre-chilled, or prepared, hyacinth bulbs saves you a step. But chilling them yourself gives you better control over the bloom time. It also lets you choose freely from the numerous hyacinth varieties.
Depending on the variety, hyacinths need to be chilled in a dark place for 12 to 14 weeks, during which they develop roots. A good root system is crucial for the bulbs to bloom.
Once you move the hyacinths to a bright, warmer location, the leaves will start growing. At that point it will take about three more weeks until they flower. For example, if you start chilling the bulbs in early November, you can expect the hyacinths to bloom in the first half of March.
Potting Hyacinth Bulbs for Chilling
After you purchase your hyacinth bulbs in the fall, pot them promptly. If that is not possible, you may store them in the refrigerator for a few days. But make sure to keep them away from apples and other fruit, as the ethylene gas exuding from ripening fruit has an adverse effect on the embryonic flower in the bulb. Place the bulbs in a perforated plastic bag with a damp paper towel to prevent them from drying out.
For potting, you need sterile potting soil and special bulb pots ideally made of clay. With their broader base and lower height than standard pots, bulb pots are specifically designed with top-heavy forced bulbs in mind. A 4-inch diameter pot is large enough for a single bulb, and you can usually fit three bulbs in a 6-inch diameter pot.
Fill the bulb pot about halfway up with potting soil, and place each bulb with the root side down in the soil. Add more potting soil until just the bulb tips stick out of the soil. Make sure the bulbs are not entirely covered with soil. Then gently push down the soil, so it is at least half an inch below the rim of the pot. This prevents the soil from washing out when watering. Finally, water the pots thoroughly.
Don’t forget to label your pots. Also, add the date of planting before moving them to their winter location for chilling.
Chilling Hyacinth Bulbs
The location to chill hyacinth bulbs needs to be dark, moist, and have a consistent chilling temperature between 40 and 45 degrees Fahrenheit. If you live in a climate with mild winters where the bulbs won’t freeze, you can keep them in a trench, cold frame, or greenhouse. Cover them with a thick layer of mulch or a thick pile of dry leaves to protect them from sunlight and to insulate them against temperature fluctuations. In colder climates, you can store the bulbs in a root cellar, unheated basement, garage, or porch.
During chilling, it is important that you never let the bulbs dry out. Water them moderately to keep the soil moist, but avoid excess moisture.
Growing Hyacinths Without Soil
Hyacinths can also be placed in jars or special forcing glasses for chilling. Forcing glasses are shaped like an hourglass, so the bottom of the bulb stays dry and the roots reach into the water below.
Another soilless way of growing hyacinths is to fill a bowl with 2 to 3 inches of pebbles. Place the bulb on top, root side down. Then, fill with more pebbles, just like you would with soil, until only the top third of the bulb sticks out. Pour in enough water, so the bottom of the bulb sits just above the water; it will grow roots that reach into the water. Make sure the bottom of the bulb is not sitting in water or else it will rot. Keep the water constant at that level, refilling as needed.
The temperature and light requirements are the same as for hyacinths grown in potting soil.
Forcing Hyacinth Bulbs to Bloom
With soilless hyacinths, it’s easy to tell when they have developed a healthy root system. But if you grow hyacinths in potting soil, watch out for white roots poking out of the drain hole of the pot. This tells you the bulbs are ready to be moved out of their cold storage. Note that pale green shoots emerging from the tips aren't enough of a sign that the bulbs are ready; it's all about the roots.
Move the hyacinths to a cool room with temperatures around 60 degrees Fahrenheit and low to medium light. In a few days, the shoots will turn into green leaves. Then, you can move the hyacinths to a brighter location but not to direct strong sunlight, which will shorten the bloom time and fade the colors. Hyacinths bloom the longest when the room temperature does not exceed 70 degrees Fahrenheit.
Keep the plants well watered. There is no need to fertilize them. Rotate the pots, so the hyacinths grow straight and don’t tilt towards the light.
Hyacinths that are grown indoors, unlike their counterparts in the garden, won’t bloom for a second year. So discard the bulbs after the bloom.