Growing Green

By Robin Trott, Extension Educator

Garden centers have put their fall bulbs on sale, and there is still time to purchase some for indoor forcing projects. Forcing flower bulbs indoors is an excellent way to brighten the cold, gray days of winter. Choose bulbs that are large, firm, and unblemished. Large, high quality bulbs produce the largest, most attractive flowers.

Most bulbs are forced in a well-drained potting mix. Almost any container is suitable as long as it has one or more drainage holes and is twice as deep as the bulbs to be planted. The first step in planting is to partially fill the container with potting soil. Then place the bulbs on the soil surface. Adjust the soil level until the bulb tips are even with the rim of the container. Generally, three hyacinths, three to five daffodils, five to seven tulips, or 10 to 12 crocuses will fit in a 6-inch-diameter pot. Once the bulbs are in place, add additional potting soil until the bulb tips show just above the soil surface. The level of the potting mix should be ½ to 1 inch below the rim of the container. After potting, water each container thoroughly. 

After planting, the potted bulbs need to be exposed to temperatures of 40 to 45°F for 12 to 16 weeks. The bulbs will not bloom properly without the cold period. The best places for cold storage are a refrigerator, or a cool basement or garage. For best results, do not allow the bulbs to freeze, water the bulbs regularly throughout the forcing period and keep them in complete darkness. If chilling in a refrigerator where apples or other fruit are also being stored, first place the potted bulbs in a plastic bag. Ripening fruit, such as apples, give off ethylene gas that can inhibit flower development and plant growth. During cold storage, remove the plastic bag containing the potted bulbs approximately once a month. Open the bag for 1 to 2 hours to allow for air exchange, then reseal the plastic bag and place it back in the refrigerator. 

When the cold period is complete, the bulbs should have shoots that are one to two inches tall. Bring sprouted bulbs out of refrigeration into a sunny spot where the temperature is between 55 and 60ºF. (At warmer temperatures, bulbs may grow faster, but flowers will not last as long.) Shoots initially will be white, but will turn green when the bulbs are brought into the light. Most bulbs will bloom about three to four weeks after they are removed from the cold. Keep bulbs moist, but not overly wet. Bulbs will require more water as leaves begin to grow rapidly.

Two of the easiest bulbs to force are amaryllis and paperwhites because they need no cold treatment. Amaryllis bulbs can be purchased pre-planted in pots or unpotted. When purchasing unpotted amaryllis bulbs select large, solid bulbs. The largest bulbs often produce two flower stalks. Gardeners can choose from single-flowering, double-flowering, and miniature varieties. Flower colors include red, pink, orange, salmon, white and bicolor. 

When planting an amaryllis bulb, select a pot which is approximately 1 to 2 inches wider than the diameter of the bulb, with drainage holes in the bottom. Plant the bulb in a well-drained potting soil. Add a small amount of soil in the bottom of the pot, center the bulb in the middle of the pot, then add additional soil, firming it around the roots and bulb. When finished potting, the upper one-half of the bulb should remain above the soil surface. Also, leave about one inch between the soil surface and the pot’s rim. Water well and place in a warm (70 to 75 degree) location. After the initial watering, allow the soil to dry somewhat before watering again. Keep the soil moist, but not wet. When growth appears, move the plant to a sunny window and apply a water-soluble fertilizer ever two to four weeks. As the plant grows, turn the pot each day to keep the flower stalk growing straight. Flower stalks that lean badly will need to be staked. Flowering usually occurs about six to eight weeks after potting. When the amaryllis begins to bloom, move the plant to a slightly cooler (65 to 70-degree Fahrenheit) location that doesn’t receive direct sun to prolong the life of the flowers. 

Paperwhites produce clusters of small white, yellow, or orange flowers on 12- to 18-inch-tall stems. The flowers of most varieties produce a moderate to strong musky fragrance. Paperwhite bulbs can be forced in clear, shallow bowls (no drainage holes) or pots. When forcing paperwhite narcissus in bowls, partially fill the container with washed gravel or stones. Place the bulbs on the gravel or stones. Then place additional gravel or stones around the bulbs, leaving the tips of the bulbs exposed. Add water to the bowl until it touches the bottom of the bulbs. Maintain the water at this level throughout the forcing period. When forcing paperwhites in pots, partially fill the container with potting soil. Place the bulbs on the soil surface. Then add additional potting soil. When potted, the tips of the bulbs should stick above the potting soil. Water thoroughly, and keep the potting mix moist throughout the forcing period. Place the planted bulbs in a cool (50 to 55-degree Fahrenheit), dark location for one to two weeks to encourage root growth. When the shoots reach a height of 3 inches, move the plants to a sunny window with a temperature of 60 to 70 degrees. As the plants continue to grow, staking is often necessary as the plants are rather floppy. Flowering typically occurs three to six weeks after potting. When the paperwhites begin to flower, move the plants from direct sunlight to prolong their bloom period. 

For more information about forcing bulbs, visit: https://extension.umn.edu/planting-and-growing-guides/growing-bulbs-indoors.

Until next time, happy gardening!