The cleome, also referred to as a spider flower, is a tall annual flower that sports long, sharp foliage and pronged blooms in shades of pink, lavender or white. This South American native thrives in hot weather and a variety of soil conditions. When left to its own devices, the cleome will freely reseed when the seedpods reach maturity. Whether you choose to use the cleome as a bold centerpiece or a stunning back border, this eye-catching annual will not disappoint.
Place 1/2 cup of lightly moistened sand or vermiculite in a plastic storage bag. Insert several cleome seeds into the medium, press out excess air and seal the bag. Store the bag in the refrigerator for one to two weeks before planting. The process, known as stratification, prepares tougher seeds for germination. Indoor germination should begin four to six weeks before the last frost for your region.
Measure out enough soil to fill the seed tray into a bucket and stir in one cup of warm water to moisten. Fill the seed tray with moistened soil, then sow seeds at least 1 to 2 inches apart across the surface. Cover seeds with a thin layer of soil to begin the germination process.
Place the seed tray in a location with several hours of sunlight and use growing lamps for added heat. Cleome seeds need temperatures of at least 80 to 85 degrees during the daytime. During night hours, lower the temperature to at least 65 degrees.
Lightly water the seed tray each morning with warm water to increase soil temperature. Keep soil moist but not soggy during the germination process.
Allow cleome seedlings to develop four sets of true leaves, then transplant each one into its own container for further development. Add moistened potting soil to individual containers and make a well in the center of each container large enough to hold the transplanted seedling.
Remove the seedling from the seed tray. If you are using a sectioned seed tray, use a butter knife to gently loosen the soil from the container, then press up from the bottom of the section to push the seedling plug upward. If you are using a flat seed tray, gently cut a 2-inch square around each seedling, then pry the plug up with the knife to remove it from the tray. Gently grab the plug, place it in the new container, then pat soil around it to cover up to the base of the seedling. Lightly water each container and return it to the growing area.
Maintain germination temperatures until the seedlings are ready to be planted outdoors. Make sure that outdoor soil temperatures are at least 50 degrees at night before transplanting.