Why Are My Marsilea Leaves Curling?

Water level and desiccation

In pond cultivation, falling water levels are the most common cause of marsilea leaf curl. Marsilea fronds grow on long petioles (leaf stalks) from a rhizome in the mud or shallow water at the pond margin. When water levels drop and the rhizome is exposed to air, the exposed petioles dry out and the fronds curl rapidly. In hot summer weather, pond water levels can drop significantly through evaporation, and the rhizomes at the pond margin are particularly vulnerable.

What to do

• Top up the pond water level regularly in hot, dry summer weather to maintain consistent coverage over the rhizome. Marsilea grown at the pond margin benefits most from keeping the planting depth at 5 to 10 centimetres of water above the rhizome.
• Plant marsilea in a planting basket on a submerged shelf, which allows the water depth to be adjusted easily by repositioning the basket as water levels change seasonally.
• If marsilea fronds have curled from desiccation, replenishing the water level allows new fronds to emerge, though severely desiccated fronds do not recover and should be removed.

Direct sun

While marsilea requires reasonable light to grow well, intense direct sun on the emergent fronds above the water surface causes rapid desiccation and curling. The thin four-leaflet fronds dry out quickly in direct summer sun, particularly if air temperatures are high and wind increases the rate of moisture loss. In pond conditions, the fronds may also fold up and close at night (a behaviour called nyctinasty, also seen in clover), which should not be confused with stress curl.

What to do

• Position marsilea in a spot receiving morning sun but afternoon shade, or in dappled light from overhanging vegetation. A location that receives 4 to 6 hours of light per day without intense afternoon sun provides suitable conditions.
• In very hot, exposed ponds, some shading from aquatic plants with floating leaves (such as water lilies or water hyacinth) reduces the intensity of sun reaching the marsilea fronds and helps maintain good growth.

Water quality (aquarium)

In aquariums, poor water quality, nutrient deficiency, or insufficient light cause marsilea fronds to curl, yellow, and die back. Marsilea is typically kept submerged in aquariums where it grows as a low carpet plant. When grown submerged, the fronds are smaller and more delicate than the emergent form. Insufficient light causes elongated, pale growth with curling fronds. Iron or nitrogen deficiency causes yellowing and slow growth.

What to do

• Provide moderate light intensity for submerged marsilea: at least 20 to 30 lumens per litre, running for 8 to 10 hours per day. In low-light aquariums, marsilea grows slowly and produces elongated, curling fronds reaching upward toward the light source.
• Use a comprehensive aquarium fertiliser to supply iron and other micronutrients consumed by the growing plant. Regular water changes replenish trace elements and dilute waste products that accumulate in the water column.

Cold temperatures

Marsilea quadrifolia is reasonably hardy in UK ponds and survives winter in the mud at the base of the pond, dying back to the rhizome in autumn and re-emerging in spring. The emergent fronds are killed by the first frosts, and the plant can be sensitive to cold water in early spring before the water temperature has warmed adequately. In aquariums, temperatures below 15 degrees Celsius cause marsilea growth to slow and fronds to curl and yellow.

What to do

• In ponds, ensure the planting basket is positioned deep enough in the pond that the rhizome zone does not freeze in winter. Positioning in at least 20 to 30 centimetres of water below the frost line is usually sufficient in UK winters.
• In aquariums, maintain water temperature above 18 degrees Celsius for tropical marsilea species, and above 12 degrees Celsius for the hardier Marsilea quadrifolia. Use a reliable aquarium heater in autumn and winter.

Pests

Marsilea in ponds can be grazed by pond snails, which eat the frond tissue and create ragged holes. Fish such as goldfish and koi also graze on the emergent fronds and can completely defoliate a marsilea planting. In aquariums, herbivorous fish have the same effect. Aphids can occasionally infest the emergent fronds above the water surface in warm weather.

What to do

• Protect pond marsilea from snail grazing by positioning the planting basket so the rhizome and stem bases are submerged while the fronds float near or above the surface, making grazing more difficult for bottom-feeding snails.
• In aquariums with herbivorous fish, marsilea is not a suitable plant choice as the fish will consume the fronds faster than the plant can replace them. Use marsilea with fish species that do not eat plants (small tetras, corydoras, shrimp).

Frequently asked questions

Why are my marsilea leaves curling?

Marsilea leaves curl most often from insufficient water depth, changes in water level, or direct sun causing desiccation. Marsilea (water clover) is an aquatic fern whose distinctive four-leaflet fronds resemble a four-leaf clover, growing on long petioles from a creeping rhizome in shallow water or wet mud at pond and streambank margins. Several species are grown as ornamental aquatic plants in UK ponds and aquariums. When grown as a marginal plant in ponds, the fronds unfurl above the water surface and are susceptible to drying out and curling in hot, direct sun or if the water level drops below the rhizome.

Is marsilea a fern?

Yes, marsilea is a true fern, though it looks very different from most ferns. It belongs to the family Marsileaceae, a family of aquatic and semi-aquatic heterosporous ferns that reproduce via specialised spore-bearing structures called sporocarps rather than the usual fern sori. The distinctive four-leaflet fronds resemble clover (Trifolium), earning marsilea the common name water clover, but the plant is entirely unrelated to clovers. The frond structure with its four symmetrical leaflets is unique among ferns and makes marsilea one of the most recognisable aquatic plants despite its unusual appearance for a fern.

How deep should marsilea be planted in a pond?

Marsilea is best planted as a marginal aquatic plant in very shallow water of 5 to 15 centimetres depth, or in wet mud at the pond edge where the rhizome is permanently moist or submerged. In deeper water, the petioles elongate to reach the surface, producing a more delicate, less compact plant. In aquariums, marsilea can be grown fully submerged, where the fronds develop a smaller, more delicate submerged form. The most commonly available species in the UK are Marsilea quadrifolia (common water clover), Marsilea mutica, and Marsilea hirsuta, which vary in their leaf size and hardiness.

Is marsilea hardy in UK ponds?

Marsilea quadrifolia (common water clover) is reasonably hardy in UK ponds and can survive UK winters in most areas if the rhizome is kept frost-free at the bottom of a pond or in very wet mud that does not freeze solid. In a garden pond of sufficient depth (at least 30 centimetres deep in the planting zone to avoid the rhizome freezing), marsilea overwinters successfully and re-emerges in spring. In very shallow ponds or pond shelves that may freeze in hard winters, the rhizome can be brought indoors for winter and replanted in spring. Marsilea hirsuta (hairy water clover) from Australia is less reliably hardy and is best treated as a tender annual or overwintered indoors in most UK gardens.