Plants aren’t growing in my natural swimming pool: the 7 causes and how to accelerate their growth without feeding algae

In a natural pool, plants are not decoration: they are part of the purification system. When they remain stunted, turn yellow, or disappear, the water quickly suffers. The paradox is well known to installers: a natural pool is deliberately designed to be low in nutrients to deprive algae of food, while plants must still manage to grow in this nutrient-poor environment. Here is why they sometimes struggle to get started, and how to help them without opening the door to algae.

The 7 most common causes

Feed plants without feeding algae

This is the essence of a natural swimming pool. In an ornamental pond, you plant in aquatic potting soil. In a regeneration zone, the substrate is often entirely mineral, gravel or lava rock, to avoid enriching the water. Young plants may sometimes struggle to get started there. The golden rule: anything supplied to the plants must remain at root level, never in the open water. In practice, surround the root ball with a small handful of specific substrate for aquatic plants, or push a slow-release fertilizer tablet deep into the gravel near the roots when planting. Never use liquid fertilizer or garden fertilizer.

Choosing plants that thrive

Native and vigorous species establish best in the poor conditions of a natural swimming pool: yellow flag iris, water mint, purple loosestrife, marsh marigold along the edges, flowering rush, bur-reed, and in deeper water, water lilies and submerged plants such as Eurasian watermilfoil or coontail. Avoid species with highly aggressive rhizomes, such as common reed, in small installations: they can invade the swimming area and, in some cases, damage the waterproofing. And of course, ban invasive exotic species prohibited in the European Union.

Animals that slow growth

Sometimes plants grow very well, but someone eats them. Ducks and coots readily graze on young shoots and pull up freshly planted specimens. Fish, if there are any after all, dig up the roots while searching through the gravel. Muskrats, in regions where they are present, may also attack rhizomes. If you notice cleanly cut stems or uprooted plants, temporarily protect young plantings with a net until they are firmly rooted.

Speeding up growth: what works

1. Plant densely: more plants initially means faster coverage.
2. Plant early: from April to June, to take advantage of the entire growing season.
3. Respect planting depths: a bank plant that is submerged will not grow.
4. Stabilize the roots: place a pebble on the root ball in areas with current.
5. Maintain mineral-rich water: adequate hardness also helps plants.
6. Prune at the end of the season to encourage vigorous regrowth in spring.

When should you be concerned?

Yellow leaves at the end of the season or a few plants lost during the first year are not alarming. However, a regeneration zone that remains sparse after two seasons does not purify the water sufficiently: algae will eventually take advantage of this. In that case, rethink the planting with your installer or with us: density, choice of species, substrate and flow distribution.

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Frequently asked questions

— How long does it take for a regeneration zone to become well planted?

It often takes two seasons to achieve dense coverage.

— Can you add fertilizer to a natural pool?

Only use slow-release tablets buried near the roots, never liquid fertilizer in the water.

— What is the best time to plant?

From April to June, when the water warms up.

— My plants turn yellow in summer, why?

Often a lack of nutrients at the roots, sometimes water that is too warm or a current that is too strong. Check the depth and add a fertilizer tablet near the roots.

In summary

• A natural pool is nutrient-poor by design: plants establish slowly.
• Plant early, densely, at the right depth and with vigorous native species.
• Feed the roots, never the water: use specific substrate or buried tablets.
• Protect young plantings from ducks and coots if necessary.
• A sparse area after two seasons should be replanned.

Last updated: September 28, 2026.