Cleome, also known as spider flower, adds bold height and whimsical blooms to summer gardens. With tall stems, airy foliage, and unique flowers in pink, white, or lavender, cleome thrives with minimal care once established. Starting cleome from seed is easy and rewarding. With the right timing and conditions, you can enjoy a summer full of flowers and even let them reseed for next year. This guide will help you grow cleome from seed with success by covering how and when to plant by zone, how to prepare the soil, light and water needs, fertilizer tips, and how to let them self-seed.
When and How to Plant Cleome by Zone
Cleome grows as an annual in most zones. It does not survive frost, so timing your planting is important. You can start seeds indoors or sow them directly in the garden.
If you live in zones 3 to 6, start seeds indoors 6 to 8 weeks before your last frost date. These zones usually have late frosts, so waiting until the soil warms up before transplanting is key. Sow seeds in trays or small pots filled with a seed-starting mix. Cover lightly with soil, press gently, and keep moist. Once seedlings are 4 to 6 inches tall and the threat of frost has passed, harden them off and plant them in the garden.
In zones 7 to 10, where the last frost comes earlier, you can direct sow cleome outdoors in mid to late spring. Wait until daytime temperatures consistently stay above 60°F. Choose a sunny spot and rake the soil smooth. Scatter seeds and lightly press them into the soil. Cleome seeds need light to germinate, so do not cover them too deeply.
For zones 9 and 10, you may also try fall sowing. Cleome seeds need a period of cold to break dormancy, so planting in fall and letting them overwinter naturally can work well in warm climates.
Soil Preparation for Cleome
Cleome does best in well-drained, moderately rich soil. Before planting, loosen the soil down to 10 to 12 inches. Mix in compost to add nutrients and improve texture. Cleome tolerates poor soil, but amending with organic matter helps boost early growth.
Avoid heavy clay soils that hold too much water. If drainage is a problem, consider planting cleome in raised beds or containers. A neutral to slightly acidic pH between 6.0 and 7.0 works best for cleome.
To help germination, soak the seeds overnight in warm water before sowing. You can also chill them in the refrigerator for a few days before planting. These steps help mimic natural conditions and improve germination rates.
Light Requirements for Cleome
Cleome loves sun. To grow strong plants with lots of blooms, choose a spot that gets full sun for at least 6 to 8 hours a day. More sun means more flowers. In partial shade, plants may grow leggy and produce fewer blooms.
If you’re starting seeds indoors, use grow lights to ensure seedlings get enough light. Place the lights a few inches above the plants and keep them on for 14 to 16 hours a day. Rotate the trays often to keep seedlings growing straight.
Once cleome is in the ground, it will shoot up quickly with good sun exposure. Mature plants can grow 3 to 5 feet tall and spread 1 to 2 feet wide, so give them plenty of space.
Watering Cleome for Healthy Growth
Water cleome seeds and seedlings gently and consistently. Keep the soil evenly moist but never soggy. After germination, allow the top inch of soil to dry out between waterings. Cleome plants develop deep roots and become drought-tolerant as they mature.
Established cleome needs only occasional watering, especially in hot, dry weather. Deep watering once a week is better than light daily watering. This encourages deeper roots and stronger plants.
Avoid overhead watering once the plants are tall, as wet leaves can encourage disease. Water at the base or use soaker hoses to keep foliage dry.
Fertilizing Cleome
Cleome grows well with minimal feeding, especially if you’ve added compost when preparing the soil. If you want to give your plants a boost, use a balanced, slow-release fertilizer once a month during the growing season.
You can also feed cleome every two to three weeks with a diluted liquid fertilizer. Choose one labeled 10-10-10 or similar, and follow the instructions on the label.
Avoid overfeeding. Too much fertilizer will encourage lots of leafy growth but fewer flowers. Cleome prefers lean soil conditions once established, so less is more when it comes to feeding.
How to Let Cleome Self-Seed
One of cleome’s best features is that it self-seeds easily. If you let the flowers go to seed in late summer and early fall, you’ll likely see new plants sprouting the next spring.
To encourage self-seeding, leave some flower heads on the plant after blooming. As they dry out, they form seed pods filled with small black seeds. These will drop to the ground naturally when the pods split open.
If you want to control where cleome grows next season, collect the seed pods before they open. Store them in a paper envelope in a cool, dry place until you’re ready to replant. You can then sow them in the fall or early spring depending on your zone.
Keep in mind that cleome seeds need a period of cold to germinate. So if your winters are mild, place the seeds in the fridge for a couple of weeks before sowing. If you live where winters are cold, nature will do the job for you.
Additional Tips for Growing Cleome
Cleome rarely suffers from pests or diseases. Its strong scent deters deer and rabbits, making it a good choice for borders or as a background plant. The flowers attract bees, butterflies, and hummingbirds, which helps your entire garden thrive.
If you want bushier plants, pinch back the growing tips when cleome is about a foot tall. This encourages more branches and a fuller shape.
Cleome doesn’t need deadheading, but removing spent flowers can tidy up the plant. If the lower leaves start to yellow, don’t worry—it’s normal as the plant matures.
Mulch around the base of each plant to retain moisture and suppress weeds. Use straw, shredded bark, or leaf mulch. Keep the mulch an inch or two away from the stem to prevent rot.
Final Thoughts
Growing cleome from seed is an easy and low-cost way to fill your garden with tall, blooming plants that make a bold statement. Whether you start seeds indoors or sow them directly outdoors, cleome rewards you with continuous blooms all summer long. By preparing the soil well, providing full sun, and watering wisely, you’ll enjoy healthy plants that grow strong and tall. Letting cleome self-seed also saves time and money next year. With just a little planning, cleome can become a staple in your flower garden for years to come.
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