Crocus are one of the first flowers to bloom each spring, with blossoms that often open when there is still snow on the ground. Fortunately, we don't have to wait till spring to enjoy these glorious flowers. Growing Crocus indoors is easy to do by forcing them to bloom for the holidays or any time during the winter. For the best chance of success and the biggest, healthiest blooms, use large, firm bulbs.
To force crocus bulbs, schedule indoor planting any time between mid-September and early December. For a continuous display of color, force several bulbs and stagger the planting times. Bulbs planted in mid-September bloom in late December. Plant bulbs in mid-October for a February display of color and in mid-November for early spring blooms.
Select shallow clay or plastic pots with a depth of at least 4 inches (20 cm) and a greater width than height. As a general rule, a pot 6 inches (15 cm) wide accommodates approximately 6 to 12 Crocus bulbs, depending on the size of the bulbs. Pots constructed of other materials such as wood or ceramic are fine as long as the pots have a drainage hole in the bottom.
Crocus bulbs require a lightweight potting medium that drains well while retaining adequate moisture to sustain the bulbs. Good quality commercial potting mixtures consisting of potting soil, sphagnum moss and perlite or vermiculite are suitable. Or make your own mixture using equal parts of all 3 ingredients. Fill the pot to about 0.5 to 1 inch (1.2 to 2.5 cm) from the top.
Plant the Crocus bulbs in the potting medium with the bulbs close together but not touching. To plant the bulbs, use your finger or a stick to create a small hole for each bulb, and then place the bulb in the hole. Cover the bulbs with about 1 inch (2.5 cm) of potting medium. Crocus bulbs require constant moisture to bloom. Water deeply until water drips through the drainage hole.
In their natural environment, Crocus bulbs chill in cold soil for 12 to 13 weeks while the bulbs develop roots for blooms in early spring. To replicate these conditions indoors, place the bulbs in an unheated garage, basement or storage shed where temperatures are between 35 and 48 ° F (2 and 9 °C). A spot where the temperatures remain fairly stable is preferable. Check the potting medium regularly, watering as needed to keep the soil moist, but not soggy.
Crocus bulbs are ready to leave the cold environment when healthy roots are visible through the drainage hole. Place the pot in a cool room where the bulbs are exposed to indirect light and temperatures between 60 and 65 °F (15 and 18 °C). When you can see the color of the buds, move the pot into the room where you want to display the bulbs. Keep the pot in indirect light, and continue to keep the potting medium moist. Moving the pot into a cooler room at night prolongs the life of the blooms.
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