How to Plant Spider Flower Seeds | Timing, Depth & Care

Spider flowers (Cleome) earn their keep in a garden bed with tall stems, airy foliage, and those unmistakable wispy blooms that open from the bottom up. They grow fast, self-sow readily, and ask for little beyond warm soil and full sun. The trickiest part is getting the timing and depth right, since the seeds need warmth to germinate and dislike having their roots moved later.

When to Plant Spider Flower Seeds

The planting window depends entirely on your local frost dates. Spider flower seeds germinate best when the soil has warmed to roughly 70 to 75°F, so sowing too early in cold, damp ground is the most common way to lose a batch.

• Direct sowing outdoors: Wait until all danger of frost has passed and the soil has warmed. This works well for most gardeners since spider flowers resent root disturbance during transplanting.
• Starting indoors: Sow seeds 6 to 8 weeks before your last expected frost date. Use individual pots or cells so the roots stay undisturbed when you move them out.

Seedlings started indoors need to go out only after the weather has settled and they have been hardened off. The University of Wisconsin Extension notes that transplanting should happen before flowering begins. If you miss that window, direct sowing next season is the safer bet.

How Deep to Sow and How to Space Them

Spider flower seeds need light to germinate, so do not bury them. Press them onto the soil surface or cover them with no more than about a quarter inch of fine soil or vermiculite.

Keep the seedbed moist but not waterlogged until sprouts appear. Germination typically takes 7 to 14 days, depending on soil temperature and seed freshness. Clemson University’s extension service reports seedlings emerging in that range, while Missouri Extension cites a slightly narrower window of 10 to 12 days.

Once seedlings have their first true leaves, thin them to 10 to 15 inches apart. Wisconsin Extension suggests at least a foot of space, and up to 3 feet if you want bushier, fuller plants. Crowded spider flowers grow weak and spindly, so resist the urge to let them all stay.

Light, Soil, and a Note on Old Seed

Full sun is non-negotiable for spider flowers. They will tolerate light afternoon shade in hot climates, but six or more hours of direct sun gives the sturdiest stems and the most blooms. Use moist, well-drained soil — this plant has no tolerance for standing water around its roots.

One detail most planting guides skip: spider flower seed is relatively short lived. Wisconsin Extension warns that germination quality declines noticeably after about 12 months of storage. If you are using seed from last season, sow it a little thicker to account for lower viability.

For the Queen series specifically, Clemson notes a brief chill improves germination. If you are growing that strain, refrigerate the seed for 4 to 5 days before sowing. Most other spider flower varieties germinate fine without this step.

If you are shopping for seed and want to compare the best options for your garden, our roundup of the best spider flower seeds to buy breaks down the top picks by variety and growth habit.

Bloom Time and Common Mistakes

Plan for patience. Clemson reports spider flowers bloom roughly 70 to 80 days after germination, so a late-sown batch may not flower until late summer. Early indoor starts push that bloom window into midsummer.

The two failures that account for most disappointing results:

• Sowing too early. Cold, wet soil delays germination or rots the seed entirely. Wait for consistent warmth.
• Overcrowding. Thin boldly. Cramped spider flowers flop over and bloom sparsely, while properly spaced plants stand tall without staking.

Spider flowers also self-sow freely. If you let a few seed heads mature in fall, expect volunteers next spring — thin those too, or move them while they are still small.