How to Grow Cleome (Spider Flower): The Self-Seeding Annual That Grows 5 Feet Tall and Blooms Until Frost

Cleome doesn’t slow down. While most bedding annuals need deadheading, division, or a second sowing to keep the color going past July, a single cleome plant just keeps opening new flowers at the top of its stem right through the first hard frost — sometimes reaching five feet tall in the process. That same vigor is also its biggest catch: cleome self-seeds so efficiently that an unmanaged patch can double its footprint in a single season, and the older, spidery-flowered varieties come with genuine thorns along the stem. None of that makes cleome hard to grow — it makes it a plant you need the right expectations for. This guide covers the mechanism behind its non-stop bloom, how to pick a cultivar that matches your garden, the regional differences between growing it in the UK and the US, and a diagnostic table for the handful of problems it does get.

Why Cleome Blooms Non-Stop From June Until Frost

Cleome’s non-stop bloom isn’t about flower longevity — it’s about stem architecture. Cleome flowers form on an indeterminate raceme: each stem keeps producing new flower buds at its growing tip for as long as that tip stays active, while the flowers lower down finish and set seed pods. Clemson Cooperative Extension describes the individual flower clusters as 4 to 8 inches long, opening from the bottom and progressing upward along the stalk as the season goes on [2]. Because the growing tip never “decides” it’s done — unlike a determinate bloomer that flowers once at a fixed point and stops — a healthy cleome plant can flower from June straight through the first frost [1][2].

That mechanism also explains a common point of confusion. Some growing guides say cleome is self-cleaning and needs no deadheading; others recommend deadheading to keep it flowering. Both are partly right: because the bloom architecture doesn’t depend on removing spent flowers, cleome keeps producing new buds either way. But the Royal Horticultural Society notes that regular deadheading measurably extends the flowering window from mid-summer through autumn [6] — it isn’t required for continuous bloom, but it redirects energy away from seed production and toward more flowers, which matters if you also want to keep the self-seeding in check.

Where to Plant It: Sun, Soil, and the Sheltered-Spot Rule

Give cleome at least six hours of direct sun a day. It tolerates everything from clay and loam to shallow, rocky soil as long as drainage is decent, and it handles occasional dry spells once established [3][4]. Overwatering and heavy feeding are the more common mistakes — both push cleome into soft, leggy growth instead of the sturdy, upright habit it’s known for [1].

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Site selection matters more than soil prep. Cleome’s strong taproot anchors it well enough that staking usually isn’t necessary [2] — but that taproot only stabilizes the base, not the flower head swaying five feet above it. In an open, wind-exposed spot I tried one summer, even mature plants leaned hard after a single thunderstorm; moving the bed against a fence line the next year solved it completely. The RHS makes the same point from the other direction, recommending a sheltered position specifically because cleome’s height makes it vulnerable to wind damage in exposed beds [6]. If you’re working with a windy site, plant cleome toward the interior of a border rather than along an exposed edge, or pick a compact cultivar under three feet (see the comparison table below).

Starting Cleome From Seed: Direct Sow vs. Indoor Start

In most of the US, direct sowing is simpler and just as effective as starting indoors. Wait until all danger of frost has passed, then sow into soil that’s reached 70 to 75°F — cleome germinates in 7 to 14 days at that temperature, and you can expect the first blooms roughly 70 to 80 days after germination [2]. Space seeds 4 to 6 inches apart and thin seedlings to 10 to 15 inches once established [2]; if you want compact, bushy plants rather than tall single stems, pinch the growing tip once young plants have a few sets of true leaves [1]. For an earlier start, sow indoors 6 to 8 weeks before your average last-frost date instead [1] — our direct-sow-versus-transplant guide covers the tradeoffs if you’re deciding between the two approaches for your whole garden plan, not just cleome.

UK growers are working with a shorter, cooler window, and cleome doesn’t forgive it well: the RHS classifies cleome as half-hardy, meaning it won’t survive frost and dislikes cold, damp soil even before that point [6]. Rather than starting indoors and transplanting at a larger size — the approach that works fine for most US gardeners — the RHS specifically recommends sowing cleome directly where you want it to grow, or moving seedlings only when they’re still very small, because the plant is unusually sensitive to transplant shock [6]. If your UK growing season is tight, treat cleome as a plant for a sheltered, sun-baked spot rather than trying to push an early start.

Thorny Heirlooms vs. Thornless Hybrids: Which Cleome to Buy

Not every cleome is the thorny, musky-scented plant your grandmother grew. Plant breeders have spent the last two decades working specifically to remove the two traits gardeners complain about most — the spines and the smell — and in the process created cultivars that behave almost like a different plant. The table below is built around one question: do you want cleome to spread on its own, or stay exactly where you planted it?

If you want a plant that fills in gaps on its own year after year, choose a Queen series and let a few seed pods mature and drop before deadheading the rest. If you’d rather cleome stay exactly where you put it — a common priority in small gardens or near walkways where thorny stems are a real hazard — the sterile Señorita and Sparkler hybrids give you the same height and flower shape without the maintenance tradeoff [1][2][4][6].

The Self-Seeding Problem: Why It Happens and How to Control It

Cleome’s self-seeding isn’t accidental spillover — it’s a deliberate dispersal mechanism built into the seed pod itself. As the elongated pods dry on the plant, internal tension builds inside the pod wall until it splits open, flinging the small round brown seeds outward from the parent plant, a dispersal method NC State Extension describes simply as pods that “pop open” in fall [3]. It’s likely related to the same defense chemistry behind cleome’s musky scent in older varieties: cleome belongs to the plant family Cleomaceae, the closest evolutionary relative of the mustard family Brassicaceae, and peer-reviewed genomic research confirms both families produce glucosinolates — sulfur-based compounds tied to the smell of mustard and cabbage — as part of their shared ancestry in the order Brassicales [7].

The practical fix is straightforward and doesn’t require giving up cleome’s self-sufficiency entirely: cut off spent flower spikes before the seed pods fully dry and split, which the RHS confirms also extends the bloom period [6]. The first time I grew Queen series cleome from a neighbor’s saved seed, I didn’t deadhead a single pod — by the following spring, volunteer seedlings had claimed roughly three feet of bed on either side of the original planting. That’s not necessarily a problem if you want a self-sustaining patch, but it’s worth deciding on purpose rather than discovering it in May.

Common Cleome Problems

Cleome is genuinely low-maintenance, but it isn’t problem-free. Most issues trace back to overwatering, humidity, or one regional pest:

All of the above draws on Clemson’s and UF/IFAS’s documented pest lists for cleome [2][4].

Pollinators, Deer, and Pets: Who Cleome Attracts (and Who Leaves It Alone)

Cleome’s flowers are built for long-tongued visitors: NC State Extension lists bees, hummingbirds, and butterflies among its regular visitors [3], and it’s frequently grown specifically as a hummingbird plant — worth pairing with our guide to annual flowers that attract hummingbirds if you’re building a wildlife bed. Deer and rabbits generally leave it alone, likely thanks to the same musky scent and, in older varieties, the thorny stems that make it unappealing to browse [1][3] — if deer pressure is a real problem in your garden, cleome pairs well with the other picks in our deer-resistant flowers guide.

For household safety: the ASPCA lists spider flower (Cleome hassleriana) as non-toxic to dogs, cats, and horses, with no records of toxic ingestion [5]. That makes it a reasonable choice around pets, though the thorny stems on Queen series and other heirloom varieties are a separate, physical hazard worth considering if you have a dog that likes to push through planting beds. If pet safety is a priority for your whole garden plan, see our dog-safe annual flowers guide.

Frequently Asked Questions

Does cleome need to be deadheaded?

Not strictly — its indeterminate bloom habit means new flowers keep opening at the stem tip regardless. But deadheading extends the bloom period further, according to the RHS, and it’s the main tool for controlling self-seeding [6].

How tall does cleome actually get?

It depends heavily on the cultivar. Traditional Queen series and similar heirlooms typically reach 3 to 5 feet, with some tall selections reported up to 6 feet; compact cultivars like ‘Linde Armstrong’ stay under 2 feet [1][2][3].

Is cleome invasive?

Not in the sense of escaping into wild habitat and displacing native species — it’s better described as a vigorous garden self-seeder. Left undeadheaded, it readily reseeds within your own beds, which is a maintenance consideration rather than an ecological one [1][3].

Can I grow cleome in a container?

Compact, thornless cultivars like Señorita Rosalita or ‘Linde Armstrong’ are better suited to containers than the taller heirloom types, which need more root room and are prone to leaning in pots [1][4].

Is cleome safe for pets?

Yes — the ASPCA lists it as non-toxic to dogs, cats, and horses [5]. The physical thorns on older varieties are a separate consideration if pets or kids play near the bed.

Key Takeaways

Cleome rewards a little upfront decision-making more than it rewards ongoing maintenance. Pick a thorny, self-seeding Queen series if you want a naturalized patch that returns without replanting, or a sterile Señorita or Sparkler hybrid if you’d rather control exactly where it grows. Give it six-plus hours of sun, a sheltered spot out of strong wind, and average well-drained soil, and the plant does the rest — flowering continuously from early summer through the first frost, though a little deadheading buys you both a longer bloom window and fewer volunteer seedlings to deal with next spring.

Sources

• Wisconsin Horticulture (UW-Madison Extension) — “Spider Flower, Cleome houtteana”
• Clemson Cooperative Extension, Home & Garden Information Center — “Cleome or Spider Flower”
• NC State Extension Gardener Plant Toolbox — “Cleome”
• UF/IFAS Gardening Solutions — “Cleome”
• ASPCA Animal Poison Control — “Toxic and Non-Toxic Plants: Spider Flower”
• Royal Horticultural Society (RHS) — “Cleome”
• PMC (peer-reviewed) — “Genomic Origin and Diversification of the Glucosinolate MAM Locus”