Why Are My Equisetum Stems Collapsing or Curling?

Drought and water level

The hollow stems of equisetum maintain their upright posture through water pressure (turgor) rather than woody tissue. When the soil or water level around the plant drops suddenly, the stems lose turgor and collapse sideways. This is more a collapse than a curl: the stems kink at the nodes and lean or fall over rather than rolling inward as conventional leaves do. For pond-grown equisetum, a sudden drop in water level in a hot summer is the most common trigger, as the shallow rhizomes lose access to adequate water within hours of the pond level dropping.

What to do

• For pond-grown equisetum, maintain a consistent water level and top up the pond in hot weather before the level drops significantly. Position the planting basket at a depth where the rhizome is always submerged even in dry spells.
• For container-grown equisetum not in a pond, water consistently and never allow the potting mix to dry out completely. Stand the container in a deep tray of water to ensure the substrate remains wet at all times.
• Collapsed stems do not recover their rigidity once turgor is lost and the cells are damaged. Cut them back to the crown to allow fresh, upright stems to emerge from the rhizome.

Physical damage

Equisetum stems snap or kink readily at the nodes when knocked or bent by wind, visitors to the pond, or neighbouring plants falling against them. The hollow stem structure means that once a node is damaged, the stem above the break loses its water supply and collapses. Heavy rainfall or strong wind can also flatten stems if the planting is dense and the outer stems have no support from adjacent growth.

What to do

• Position pond containers of equisetum in a sheltered spot protected from strong winds. A position at the margin of a sheltered garden or beside a fence or wall provides wind protection while maintaining the damp conditions the plant requires.
• Remove any damaged stems cleanly at the base to prevent dieback from spreading to the rhizome. Equisetum will produce new stems rapidly from the rhizome once old damaged stems are removed.

Yellowing stems

Yellowing of equisetum stems most often results from iron or nitrogen deficiency, stagnant waterlogged conditions, or natural seasonal die-back. Equisetum hyemale is largely evergreen, maintaining its stems through winter, but some yellowing and collapse of older stems is normal as new growth replaces them in spring. If yellowing occurs broadly across all stems in the growing season, investigate the water and soil conditions rather than treating it as seasonal.

What to do

• Ensure the pond water is adequately oxygenated: stagnant, low-oxygen water in a pond without a fountain, pump, or waterfall can cause rhizome stress and nutrient uptake problems. Adding some water movement to the pond improves conditions for all aquatic plants including equisetum.
• For container-grown equisetum in garden soil or potting mix, a balanced slow-release fertiliser applied in spring can address nutrient deficiency. Avoid high-phosphorus fertilisers; nitrogen and iron are the most commonly deficient nutrients in waterlogged, anaerobic conditions.

Uncontrolled spread

While not a problem with the stems themselves, uncontrolled spread of equisetum rhizomes is a common issue for UK gardeners. If the planting basket cracks, or if rhizomes escape through the drainage holes of a submerged container, the plant can quickly establish in the pond substrate or surrounding soil. Established rhizomes are difficult to remove completely and can persist for years. The ornamental species Equisetum hyemale, though not legally invasive, can spread substantially from a poorly contained planting basket.

What to do

• Always grow equisetum in a solid-sided (not mesh) planting basket with no holes large enough for rhizomes to escape. Check the basket annually and replace it if cracks appear in the sides.
• Divide the plant every 2 to 3 years by lifting the planting basket, removing the rhizomes from the container, discarding the outer portions, and replanting the central clump in fresh potting mix. This controls the spread and refreshes the growth.

Container problems

In containers not placed in a pond, equisetum requires a potting mix that retains water well and must be kept consistently saturated. Standard potting mixes drain too freely and dry out too quickly for equisetum unless the container is stood in a permanent tray of water. Very compact or compacted soil in containers can exclude oxygen from the root zone and cause rhizome deterioration over time, even when the surface remains wet.

What to do

• Use a heavy, moisture-retentive potting mix for container equisetum, such as loam-based compost mixed with equal parts composted bark. Stand the container permanently in a deep tray or saucer filled with water to keep the substrate saturated.
• Repot every 2 years to refresh the growing mix and prevent compaction. The rhizomes of a well-established equisetum fill the container rapidly, and the compressed root mass in an overly full container leads to reduced vigour and yellowing of new stems.

Frequently asked questions

Why are my equisetum stems collapsing or curling?

Equisetum stems collapse or curl most often from drought, physical damage, or sudden changes in water level. Equisetum (horsetail) is a primitive, spore-bearing plant related to ferns, with hollow, jointed green stems and very reduced, scale-like leaves fused into toothed sheaths at each node. The stems perform photosynthesis and are the plant's primary above-ground structure. When conditions are inadequate, the hollow stems lose turgor and collapse or bend rather than curling in the way conventional leaves do. The most common reason for collapse is drought or a sudden drop in water level when equisetum is grown as a pond marginal.

Is equisetum (horsetail) invasive in UK gardens?

Field horsetail (Equisetum arvense) is a native UK weed and one of the most difficult garden weeds to eradicate because of its extensive deep rhizome system. The ornamental horsetails grown in garden ponds and containers (most commonly Equisetum hyemale, the rough horsetail or scouring rush) are different species that can also spread vigorously from their rhizomes and should be grown in containers sunk into the pond or set into the ground to prevent uncontrolled spread. In the wild in the UK, Equisetum arvense is a common field weed; the ornamental species are not invasive by legal classification but can spread substantially if left uncontrolled.

Why are my horsetail stems turning yellow?

Horsetail stems turn yellow most often from iron or nitrogen deficiency, waterlogged anaerobic soil, or natural die-back at the end of the growing season. In ponds with stagnant, oxygen-depleted water, the shallow rhizomes may fail to absorb nutrients efficiently, causing yellowing and slow growth. In gardens, the common field horsetail (Equisetum arvense) dies back to its rhizomes naturally in autumn, with stems yellowing and collapsing in September and October. This is entirely normal. The ornamental species Equisetum hyemale is largely evergreen, so yellowing outside of winter die-back more typically indicates a nutritional or environmental issue.

How should equisetum be grown in a garden pond?

Equisetum hyemale (rough horsetail or scouring rush) is most commonly grown as an ornamental marginal plant in garden ponds, grown in planting baskets at 0 to 15 centimetres of water depth. To control spread, always grow equisetum in a planting basket with a solid (not mesh) base and sides, or in a container sunk into the ground. The rhizomes spread vigorously if given access to open soil or pond substrate and can be difficult to remove once established in the wider garden. Regular division every 2 to 3 years keeps the plant within its basket and maintains vigorous, fresh stem growth.