Spider flower (Cleome hassleriana): why this low-maintenance flower can take over your garden

It looks harmless, needs very little care and seems ideal for gardeners who do not enjoy watering – but a year later, you may suddenly be battling a green invasion throughout the garden.

Many amateur gardeners pick up a striking annual flower at the garden centre, with huge flower clusters carried on tall stems. Its label promises a hardy, sun-loving plant that requires little water and blooms all summer long. What it does not mention is that, once planted, it can soon appear in every border, on paths and even in the vegetable patch – and be difficult to remove again.

The spider flower: a dream for low-maintenance gardening, a nightmare in year two

The plant in question has a particularly apt German name: the spider flower, botanically Cleome hassleriana. People seeing it for the first time are often impressed. Its flowers sit like small pom-poms on long, slender stems, glowing in white, pink or purple. From a distance, the flower heads can look almost like fireworks rising above the green foliage.

Its defining feature is the long stamens projecting from every bloom, which give the plant its spider-like outline. The leaves are palmately divided, slightly aromatic, and combine with the flowers to create an airy, almost exotic appearance. Planted in rows, spider flowers rapidly frame patios or fill the back of borders.

On paper, Cleome hassleriana sounds like the ideal summer flower: drought-tolerant, rarely affected by disease, and generally avoided by slugs and wildlife.

It will grow even in poor soils, manages with little watering and copes with hot spells far better than many traditional bedding plants. That is precisely why more gardeners are choosing it when lawns are being replaced or borders need to become green and colourful quickly.

Why this flower can take over your entire garden

The problem does not arise in the first year, but in the second. Spider flower is an annual species that produces seeds extremely generously. After its abundant flowering period, long, narrow pods form along the stems. They contain countless tiny seeds which, once dry, are ready to spread.

These pods burst open and scatter their contents widely around the parent plant. Some seeds remain in the border, while others are carried further by wind, rainwater or hoeing. Within a few months, the plant can quietly make its way across the whole garden.

Many gardeners describe the same pattern:

• A few purchased plants in the border during the first summer
• Large numbers of seedlings suddenly appearing around the patio, paths and vegetable patch the following spring
• A genuine “wall” of spider flowers by the third year, often in places where they were never wanted

Officially, Cleome hassleriana is not generally classed as one of the strictly defined “invasive” species in Central Europe. Even so, it can become highly self-seeding in gardens. It germinates early, grows rapidly and pushes through gaps between perennials, roses and vegetables without restraint.

How to recognise spider flower seedlings

To stop the plant early enough, you need to identify its young plants confidently. Young spider flowers initially look unremarkable, but several characteristics make them easy to spot:

• Several narrow leaflets arranged in a palmate pattern
• Clearly stalked leaves, often with slightly reddish leaf stems
• Alternate leaves along the stem
• A relatively upright habit even at the seedling stage

Once you know these leaves, you will start noticing the seedlings everywhere. That is exactly when you should act: while the plants are still small and easy to pull out.

Keeping control: how to prevent its spread

1. Remove flowers at the right time

The most effective measure begins with the plant itself. As soon as flowers start to fade, cut them off before the seed pods can develop fully. This dramatically reduces the seed bank and also extends the flowering period of the remaining plants.

Anyone wishing to tolerate spider flower in the garden must consistently “disarm” it – in other words, never allow pods to ripen.

Regular checks around the garden in high summer are ideal. Put spent flower clusters into household waste or a closed garden-waste bin, rather than on an open compost heap.

2. Remove seedlings early and thoroughly

The following spring, inspect borders and paths closely. As soon as the soil warms up, hundreds of seedlings may appear. The best approach is to:

• Pull seedlings out by hand, including the roots, when the soil is damp
• Skim off larger carpets of plants near the surface with a hoe
• Avoid composting removed plants if even small pods have already formed

Anyone who consistently removes every young plant for one season can greatly reduce the population. After two to three years, the soil is usually largely free of viable seeds.

3. On larger areas: use mulch as an ally

Where entire sections are already covered, simply weeding reaches its limits. In these areas, a thick layer of mulch helps suppress the germination of new seeds. Suitable materials include:

• Bark mulch
• Woodchip
• Straw or grass clippings, thoroughly dried first

The layer should be at least five centimetres thick. Light-sensitive seeds such as those of spider flower have far poorer chances beneath this covering.

Which alternatives are genuinely garden-friendly?

Anyone who loves the look of tall, airy summer flowers does not have to choose spider flower. Numerous species offer a similar effect without self-seeding so aggressively. Native or well-adapted perennials and annuals that also support insects are particularly worthwhile.

Possible alternatives include:

• Tall cosmos (Cosmos) – delicate foliage, large flowers, good for bees and butterflies, and relatively easy to control
• Verbena (Verbena bonariensis) – tall, transparent clouds of flowers that butterflies enjoy; it self-seeds, but only moderately
• Greater knapweed – a hardy native species for naturalistic borders
• China asters or zinnias – colourful plants with manageable self-seeding

Studies show that a relatively small proportion of native plant species provides most of the food for butterfly and moth caterpillars.

By deliberately choosing such species for borders, you create habitat for insects while also reducing the risk of introducing a difficult-to-control exotic plant.

What to look for at the garden centre generally

Spider flower is not an isolated case. Many “miracle plants” marketed to low-maintenance gardeners come with a risk: they thrive where other plants fail, and are therefore equally keen to spread. A quick check before buying can prevent a great deal of frustration later.

Ask yourself a few simple questions before buying new ornamental plants:

• Is the species known for prolific self-seeding or for producing runners?
• What happens after flowering – does it create many seed heads or underground rhizomes?
• Is it already considered troublesome or naturalised in other countries or regions?
• Does local wildlife genuinely benefit from it, or is it primarily decorative?

When in doubt, it is worth taking a quick look at gardening forums or conservation organisations before planting large quantities of a conspicuously cheap or heavily promoted “low-maintenance” plant.

Why low-maintenance does not always mean straightforward

The story of the spider flower demonstrates how misleading the promise of “low-maintenance” can be. A plant that scarcely needs watering, self-seeds and has few pest problems can also quickly slip out of control. For people who like tidy borders, clear paths and a well-organised vegetable garden, it can become a real nuisance.

Conversely, anyone who prefers a highly natural, freely growing garden and is prepared to weed regularly can use Cleome hassleriana deliberately – for example, as a temporary filler plant in unused areas. What matters is making that choice with open eyes, rather than through lack of information at the garden centre.

At a time of longer dry periods and water shortages, many people are looking for “indestructible” summer flowers. A better strategy is to combine site-appropriate, preferably native species, use mulch and care for the soil, and not trust every spectacular exotic flower promoted as “low-maintenance”. Anyone who follows this approach can avoid the later struggle against a plant that has long since decided for itself where it wants to grow.