Cleome Seeds – Cleome hassleriana

Cleome seed germination tends to go more smoothly when seeds are cold stratified in the refrigerator for about a week before sowing. Sow on or just at the soil surface and keep the area consistently moist and warm, ideally between 70 and 75 degrees Fahrenheit. Keep in mind that germination outcomes depend on a combination of factors including your local climate, soil quality, and watering consistency, so results vary from garden to garden.

Cleome hassleriana is one of the more enthusiastic self-seeding annuals you will encounter, and in many gardens it returns reliably each year without any intervention once it has been established for a season. Allowing a few plants to fully mature and drop their seeds in late summer or fall is all it takes to set up next year's display. In very cold or very short-season climates, self-seeding may be less reliable, so saving a few seeds indoors as a backup is a smart habit.

Cleome hassleriana is not listed among the severely toxic plants for dogs or cats, but it is not considered completely harmless either, and some animals may experience mild digestive upset if they chew on the foliage. The sticky, spiny stems are also a physical irritant that most pets will naturally avoid after a close encounter. If you have a pet that tends to nibble on plants, placing cleome where it is out of easy reach is a reasonable precaution, and consulting your veterinarian with specific concerns is always worthwhile.

In good growing conditions with full sun and decent soil, Cleome hassleriana typically reaches 3 to 5 feet tall, with some plants pushing toward 6 feet in particularly warm, long summers. This height makes it well suited to the back of a border where it can act as a soft, airy backdrop for shorter plants. In leaner soil or shadier spots, expect more modest growth.

Cleome performs at its peak in full sun, meaning at least 6 hours of direct sunlight per day, where it produces the most flowers and grows with a sturdy, well-branched habit. It will tolerate partial shade, but plants in lower light conditions tend to stretch toward the light, producing fewer blooms and a more open, floppy structure. If full sun is not available, aim for a spot that gets morning sun with some afternoon protection rather than deep or consistent shade.

The right time to direct sow spider flower seeds outdoors is after your last expected frost date, once soil temperatures have climbed to at least 60 degrees Fahrenheit. In many temperate climates this falls somewhere between late April and late May, though your specific timing depends on your hardiness zone and local spring conditions. Sowing too early into cold soil tends to delay germination and can reduce how many seeds successfully sprout.

Cleome is genuinely one of the more effective pollinator garden flowers you can add to a summer border, drawing consistent visits from hummingbirds, swallowtail butterflies, bumblebees, and hawk moths, particularly in the evening when its fragrance intensifies. The long-tubed flowers and nectar-rich blooms are especially well suited to pollinators with longer tongues or hovering flight. Planting cleome in a sunny, sheltered spot and allowing it to bloom over its full season gives pollinators an extended food source through the heat of summer.