Fasciation: Why Plant Stems Go Flat and Curled

Fasciation is one of the oddest things you’ll see in the garden. A stem suddenly grows flat like a ribbon, several flowers fuse into one crested lump, or a flower spike spreads into a fan. It’s natural to worry it’s a disease, but almost always it isn’t. It’s just a growth quirk, usually a one-off, and the rest of the plant carries on as normal.

Here’s what it is, what sets it off, which plants get it most, and when it’s worth cutting out.

What fasciation is and how it forms

Fasciation is when stems or flowers grow flattened, widened, fused or curled. The name comes from the Latin for a band or ribbon, which sums it up nicely.

It starts at the growing tip, the tiny point at the end of a shoot where new growth is made. Normally that’s a single neat point. In fasciation it spreads out sideways into a line, so the stem it makes comes out flat. On flowers, several can merge into one crested head, or a spike can widen into a flat mass.

The good news is that fasciation stays local. Only the shoot where the tip went wrong is affected. Every other stem, leaf and root carries on as normal, which is why it rarely does any harm. That’s quite different from the whole-plant colour problems in our guide to chlorosis and yellow leaves.

A normal growing tip stays a single point. A fasciated one spreads sideways into a flat ribbon.

Classic fasciation on forsythia. One stem has gone flat, while the stems around it grow normally.

What causes fasciation in UK gardens

There are a few possible causes, and most are harmless. Knowing which one you’ve got tells you whether to bother doing anything.

The most common is pure chance. Something goes wrong in one growing tip, and it usually never happens again. Next is damage. A late frost, a knock, or insects or slugs nibbling a growing tip can all upset how it grows. The RHS guide to fasciation lists these and the other causes.

Less often, it’s a soil bacterium called Rhodococcus fascians. It tends to cause clusters of stunted, distorted shoots near the base of the plant. Unlike the other causes, this one can come back and can spread on tools or through cuttings. Weedkiller drift can also twist growth in a way that looks similar. Sap-sucking pests can be one cause of damage, so if you see insects as well, our guide to getting rid of aphids is worth a look.

Up close, the flat, grooved fasciated stem sits right beside a normal round one on the same healthy plant.

Which plants fasciate most often

Some plants do it far more than others. Knowing the usual suspects helps you spot it quickly.

Forsythia and euphorbia, especially Euphorbia characias, are common examples in UK gardens. Delphinium and veronicastrum can throw up a dramatically wide flower spike. Acer, prunus, lily and echinacea do it now and then too.

Some plants are even grown for it. Fantail willow (Salix udensis ‘Sekka’) is loved by flower arrangers for its curly, flat stems. Crested celosia, or cockscomb, is a bedding plant bred for its velvety, crested flower heads. So fasciation isn’t bad, just unusual. Our guides to growing forsythia, growing delphiniums and growing echinacea cover three plants that do it often.

Euphorbia is one of the most common plants to fasciate. A curiosity, not a disease.

Fasciation causes compared at a glance

Use this table to tell a harmless one-off from the rare kind worth acting on.

For the four common causes, you don’t need to do anything at all. Only the bacterial kind needs a bit of care. One simple rule covers every case: never take cuttings from a fasciated stem, just in case. After that, it’s purely down to whether you like the look.

A fasciated delphinium spike. Striking, harmless, and unlikely to happen on the same plant again.

A seasonal plan for spotting and managing fasciation

Fasciation shows up with the rush of new growth and flowers, mostly in spring and summer.

Take a photo before cutting it out

Snap a quick photo of the flat stem, its base and the healthy growth around it before you cut. It makes it easy to tell next year whether the problem has come back in the same place.

A stem that goes flat once and never again is almost certainly chance or damage. Clusters of distorted shoots coming back at the base year after year point to the bacterial kind, the only type worth removing for the plant’s sake.

Sometimes fasciation is the whole point. Fantail willow is grown for its curly, flat stems.

How to cut out fasciation if you choose to

Cutting it out is easy, and optional. The plant doesn’t need it gone, so it’s really about looks unless you suspect bacteria.

Cut the flat stem back to normal growth, just above a healthy bud or where the stem turns round again. Use clean, sharp secateurs. Then wipe the blades with garden disinfectant or an alcohol wipe, in case it was the bacterial kind. For more on technique, see our guide to pruning shrubs.

Take the flat stem back to normal growth, then clean the blades.

If you see clusters of distorted shoots at the base coming back each year, treat it as probably bacterial. Cut out the affected growth, put it in the bin rather than the compost, and don’t take cuttings or divisions from that plant. On fantail willow, do the opposite and enjoy cutting the curly stems for the house. The same quirk is a fault on one plant and a feature on another.

Common mistakes when dealing with fasciation

Most worry about fasciation comes from mistaking a harmless quirk for something serious.

• Treating it as a disease. Spraying does nothing for it.
• Digging up the whole plant. Only one growing tip is affected, so there’s no reason to lose a healthy plant.
• Taking cuttings from it. If the cause was bacterial, the cuttings carry it on.
• Not cleaning your secateurs. Cutting a bacterial case and then pruning elsewhere can spread it.
• Cutting out the good stuff. Fantail willow and crested celosia are grown for their fasciation, so know your plant first.

Now you can spot fasciation and decide whether to do anything about it. For another odd-looking problem, read our guide to chlorosis and yellow leaves, or browse the full problems section.

Frequently asked questions

What is fasciation in plants?

It’s flattened or fused growth from a growing tip that’s gone wrong. Stems widen into ribbons or fans, and flowers can merge into crests. It usually affects just one part of the plant. The rest grows normally and the plant isn’t at risk.

Is fasciation harmful to my plant?

No, it’s almost always harmless and often a one-off. The stem looks odd, but the plant stays healthy. Only the rare bacterial kind can come back and spread. Leave it for interest or cut it out, and the plant will be fine either way.

What causes fasciation?

A fault in the plant’s growing tip. That can be pure chance, frost, a knock, insect damage, or occasionally a soil bacterium called Rhodococcus fascians. Most cases are a one-off. Frost damage to young shoots after a cold spring is a common trigger.

Should I cut off fasciated growth?

Only if you don’t like how it looks. The plant doesn’t need it removed. Cut the stem back to normal growth and clean your secateurs afterwards, in case the cause was bacterial. Lots of gardeners leave fasciation on euphorbia and willow because it’s so curious.

Does fasciation spread to other plants?

Usually not, as most cases are chance or damage. Only the bacterial kind, Rhodococcus fascians, can spread on tools or through cuttings. To be safe, don’t take cuttings from affected stems, and clean your secateurs after cutting them out.

Which plants get fasciation most?

Forsythia, euphorbia and delphinium are the most common in UK gardens. Veronicastrum, acer, willow, lily and echinacea do it too. Some, like fantail willow and crested celosia, are grown on purpose for it. Any plant can do it now and then by chance.