Gunnera manicata is one of the largest, most spectacular, architectural herbaceous plants grown in our gardens. Commonly known as ‘giant rhubarb’, this plant is not related to the rhubarbs at all, although it is not difficult to see how it got its common name.

The giant leaves can grow to 6ft (1.8m) or more across and are very similar in appearance to rhubarb leaves. They grow directly from the base of the plant and have strong, prickly stems. The leaves are very rough and they can make a rasping noise under windy conditions as they brush together. The flowers are hidden away among the foliage and appear in summer as green, conical spikes which turn brown when in seed.

This is not a plant for a small garden and it prefers to grow near water, so a pond or stream will provide an ideal setting. Gunnera manicata is not a completely hardy plant and needs some form of winter protection. The shoots at the centre of the plant are frost sensitive, so these should be covered with the dead leaves or a straw mulch when frost is expected.

It is important to provide a deep, rich soil for Gunnera. Add plenty of organic material to the soil and top dress every year, with more. Apart from mulching during the winter, no other attention is required.

Growing Requirements

Position
Gunnera manicata prefers an open position but it will accept a degree of light shade from tall trees. It is best grown next to water, so extra moisture should not be needed. If planted in any other location, ensure that the ground does not dry out.

Size
Giant rhubarb will grow to a height of 6ft (1.8m) with an 8ft (2.4m) spread.

Propagation
Increase plants either from seed or by splitting off a part of the plant with a spade. Plant out in the spring, after the threat of frost has passed, so that plants can become established before the onset of winter.

Family: Gunneraceae
Genus: Gunnera

The Water Plantain is an upright, airy plant that doesn’t seem to take up as much space as its size would suggest as you can see right through its wiry branches. The flowers are pale, pinkish white when examined up close, but often appear white from a distance. The plant blooms from late spring into summer.

The foliage consists of long, oval, dark green leaves that are held on long stalks so that they stand up tall above the water. The plants form large clumps, and the flowering stems arise from this solid base of foliage. Unless it is grown beside a large natural pond, one plant would probably suffice. If it is grown in the mud rather than directly in the water, it must not be allowed to dry out. Water copiously if the water level of the pond or stream drops to keep the soil moist. These plants are hardy and need no special treatment to survive winter. Like most pond plants, it can be invasive so cut off the flower stems as the flowers fade, before they have chance to scatter seed everywhere. When cut and dried, flower stems are ideal for flower arranging.


Growing Requirements

Position
This is a plant to be grown on the edge of a pond or slow-moving stream. It will grow happily either in the mud at the edge of the water, or in water about 6 inches deep. As with most aquatic plants, the best time to plant out is in the spring, when the pond is warming up. Plug directly into the mud at the side of, or if the pond is lined, into a lattice pot. The water plantain will grow best in full sunlight. It will grow in light shade, but won’t flower so well.

Size
Water Plantains will grow to a height of 3ft (90cm) with a 2ft (60 cm) spread.

Propagation
These plants grow very readily from seed, especially if sown in a cold frame while fresh. Place the pot in about 1in (2.5cm) of water to keep the soil wet. The seedlings can be potted up when large enough to handle and kept in the cold frame for the first winter, planting out in late spring. Larger plants can be divided in the spring or autumn and the divisions planted straight out into their permanent positions.

Family: Alismataceae
Genus: Alisma