If you love the distinct strong fragrance of hyacinths (Hyacinthus orientalis), you don’t have to wait for them to poke their heads out in the spring. By coaxing their bulbs into blooming indoors, you can enjoy them a few weeks, in cooler climates even a couple of months earlier than outdoors. Hyacinths are especially suitable candidates for bringing on an early indoor bloom called forcing.
This requires a little planning ahead because in order to bloom, the bulbs need chilling—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.
You need sterile potting soil and special bulb pots, ideally made of clay. With their broader base and less height than standard planting pots, these pots are specifically designed with top-heavy forced bulbs in mind.
Fill the bulb pot about half with potting soil and place the bulbs with the root side down in the soil. A four-inch diameter pot is large enough for a single bulb, and you can fit three bulbs in a six-inch diameter pot. Add more potting soil until just the 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. Water the pots thoroughly.
Don’t forget to label your pots, and 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 F. If you live in a climate zone with mild winters where the bulbs won’t freeze, you can keep them in a trench, cold frame, or greenhouse, covered with a thick layer of mulch or a thick pile of dry leaves to protect them from sunlight and insulate them against temperature fluctuations.
In colder climate zones, 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 any 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 two to three inches of pebbles. Place the bulbs on top, root side down, and fill with more pebbles just like you would with soil, until only the top third of the bulbs 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 that the bottom of the bulbs is not sitting in water, or else it will rot. Keep the water constant at that level and refill as needed.
The temperature and light requirements are the same as for hyacinths grown in potting soil.
Forcing Hyacinth Bulbs to Bloom
In soilless hyacinths, it’s easy to tell when they have developed a healthy root system. If you grow hyacinths in potting soil, watch out for white roots poking out of the drain hole of the pots. This is the time when the bulbs are ready to be moved out of their cold storage. Pale green shoots alone emerging from the tips are not a sign that that the bulbs are ready.
Move the hyacinths to a cool room with temperatures around 60 degrees F and low to medium light. In a few days, the shoots will turn into green leaves, and you can move the hyacinths to a brighter location yet not 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 F.
Keep the plants well watered. There is no need to fertilize them. Rotate the pots so the hyacinths grow straight and won’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.