“Forcing” manipulates a bulb’s environment to simulate its natural growing cycle, prompting it to bloom outside of its typical season, often in winter. This technique allows gardeners to enjoy the fragrant, vibrant flowers of spring-blooming bulbs, like hyacinths, indoors when the weather outside is cold. Forcing relies on mimicking the cold, dark period the bulb naturally experiences underground to trigger the internal chemical processes necessary for flowering. This delivers a welcome burst of color and scent to the home during the colder months.
Preparing the Hyacinth Bulbs and Containers
Successful forcing requires selecting appropriate plant material. The most reliable hyacinths are larger sizes (16 to 19 centimeters circumference) because they hold more energy for rapid indoor growth. Purchase firm, healthy bulbs showing no signs of mold or damage. Wear gloves when handling them, as hyacinths contain oxalic acid, which can cause skin irritation.
Planting media options include traditional potting mix or specialized, well-draining bulb fiber. Alternatively, hyacinths can be forced hydroponically using specialized forcing vases or jars filled with pebbles and water. For soil planting, use a shallow container and set the bulbs close together but not touching, ensuring the pointed tip remains exposed. If using water, the bulb’s base should sit just above the water level, allowing roots to reach moisture without submerging the bulb, which prevents rot.
Implementing the Required Chilling Phase
The chilling phase satisfies the biological requirement for a cold period to initiate flower development (vernalization). Hyacinth bulbs require consistent exposure to cold temperatures, ideally 35°F to 48°F (2°C to 9°C), for a minimum of 10 to 14 weeks. This cold treatment signals the embryonic flower inside the bulb to prepare for growth.
Suitable locations for this prolonged cold exposure include a refrigerator, unheated garage, cold cellar, or protected outdoor cold frame. The environment must remain dark throughout chilling to prevent premature leaf growth. Check the soil or water weekly to maintain moisture. During this time, the bulbs develop a substantial root system, which anchors the plant and allows for water and nutrient uptake. If using a refrigerator, avoid storing bulbs near ripening fruit, as the released ethylene gas can damage developing flower buds.
Encouraging Growth and Flowering Indoors
The chilling period ends when the bulbs have developed a robust root mass and the pale shoot measures about two to three inches tall. Moving bulbs directly from cold storage into a warm, brightly lit room can shock the shoots and cause stunted growth. The transition must be gradual, starting the bulbs in a cool, low-light location around 60°F (15°C) for one to two weeks.
This intermediate step allows the shoots to acclimate and begin chlorophyll production, visible as the green color intensifies. Afterward, move the pots to bright, indirect light to encourage the flower stalk to elongate. Cooler room temperatures, ideally below 70°F (21°C), prolong the bloom period. Once the flower spike shows color, the plant can be placed in any desired location; the transition to full bloom typically takes two to three weeks.
Handling Common Issues and Post-Bloom Options
The most common reason a forced hyacinth fails to bloom is an insufficient chilling period, either in duration or temperature control. A cold period that is too short or fluctuates above 48°F may cause “blasting,” where the flower bud forms but fails to emerge. Another issue is allowing the bulb to dry out completely during the rooting phase, which limits its ability to support the flower stalk. Constant, moderate moisture throughout the chilling process is essential for success.
After flowering, the bulb is generally exhausted from blooming out of season. Allow the foliage to photosynthesize until it naturally yellows and dies back. The bulb usually lacks the reserves to be successfully forced again indoors. However, these bulbs can often be replanted outdoors for natural spring blooming in subsequent years. To prepare them, harden the bulbs off by gradually exposing them to outside temperatures before planting them into the soil in the fall.