Growing Aquatic Plants from Seed: Techniques for Waterlilies and Marginals

Raising Aquatic Plants from Seed

Many aquatic plants can be raised from seed, mostly natural species. Strains of iris and mimulus can also be increased this way. Named cultivars rarely come true and must be propagated vegetatively.

Waterlilies

There’s a trend toward growing large-flowered waterlilies from seed, but progeny always differ—mostly inferior and difficult to grow to flowering size. Recent techniques spawned this trend, but expectations are rarely met. For high-quality, large-flowered waterlilies, vegetatively propagated stock is essential.

The only waterlilies justifying seed propagation—and which can’t be increased otherwise except occasional division—are Nymphaea ‘Pygmaea Alba’ and its progenitor N. tetragona. ‘Pygmaea Alba’ produces greenish-white fruits with viable seeds after flowering. Gather and sow immediately; they ripen and germinate freely. Trick: capture seeds before dispersal. Place a tiny muslin bag over each developing pod.

Waterlily seeds are tiny, embedded in sticky gelatinous material. Don’t separate jelly from seeds—damage occurs. Sow seeds and jelly together, spreading evenly over compost. Soil-based compost is preferable to soilless types. Spread with tweezers, lightly cover with more compost. Spray gently from overhead to settle. Stand pots in warm light position in bowl/aquarium, water level just above compost.

Seedlings appear after three weeks: translucent, lance-shaped leaves resembling aquatic liverwort. Vulnerable to filamentous algae entanglement. At first sign, apply reputable algae control. If algae accumulates, kill and remove promptly to prevent rot damaging seedlings.

As seedlings develop, raise water level slightly. When first two or three floating leaves reach surface, prick out. Lift in small clumps, wash thoroughly, tease apart. Prick into seed tray/pan, immerse in water ~2.5 cm (1 in) above compost. Raise water gradually as floating leaves grow. After a season, seedlings are large enough for permanent positions.

Sowing Seeds – General Steps

1. Use clean seed compost, thoroughly soak before sowing. Spread seeds sparingly—crowded seedlings invite disease.
2. Cover with thin compost or sand. Sand is especially beneficial for waterlily seeds, discouraging algae.
3. Stand pot in water container. For waterlilies, water level just above compost. For bog/marginal plants, just below compost level.

Other Aquatics and Bog Plants

Seed is the readiest method for popular marginal aquatics and most bog garden plants. Only species come true (exceptions: Primula japonica cultivars ‘Postford White’ and ‘Miller’s Crimson’). While vegetative increase is possible, seed is most reliable and economic for more than two or three plants.

Marginals and deep-water aquatics (e.g., water hawthorn Aponogeton distachyos) should be sown fresh, sometimes still green. Water hawthorn seed must not leave water until sowing, or it perishes.

Sow true aquatics in wet, heavy loam compost. Plants with floating leaves (water hawthorn) appreciate a few centimeters of water over crowns once through soil. Don’t submerge freshly sown seeds—they’re light and float out. Thin silver sand layer holds them down and prevents algae. Once germinated and established, prick out and treat like young waterlilies.

Bog garden plants similar, though some raise in open ground—difficult due to fine seed, hostile soil, uncontrolled watering. Seed trays/pans in a cold frame are easier, yielding better quality.

Most bog plant seed best sown fresh—fine if collected, problematic if bought. Collected seed sown mid–late summer; packeted seed waits until spring. Some non-fresh seed requires chilling to break dormancy (common with primulas). Sow in good soilless compost in clean pans, place in freezer for a couple of weeks, then bring to light and warmth. Germination follows rapidly. Grow on in individual pots for season, plant out next spring.