how to grow petasites gunnera aroids

by Ruby Weinberg

The element of surprise is one way of adding excitement to a garden. A planting with over-sized leaves may be just the ticket for eliciting that surprise. “What are these plants?" visitors almost always ask. While he or she may not remember your answer, who can forget those few plants with very large leaves that survive - in a dormant state - a mid-Atlantic winter?

It was on a trip to Costa Rica many years ago that I first became captivated by “big leaves." There they were, along the roadside, the species Gunnera manicata, also called prickly rhubarb. Growing in enormous clumps, each serrated leaf was about 8 feet in circumference, so large that the peltate stems could scarcely be seen.

Some years later, imagine my surprise when I observed this same tropical species in Frank Cabot's garden, Stonecrop, in Cold Spring, New York. Stonecrop's gunnera was covered half the year with a crate and other materials to insulate it from winter cold. In Oregon, the Dancing Oaks Nursery also grows gunnera (no mail order!), but wraps them carefully when the temperature drops below 20 degrees.

Heavy coverings are scarcely worth the trouble in my own northern New Jersey garden, and so I searched for another big-leafed plant that I could easily grow. It was then that I read about Petasites japonicus var. giganteus, the largest leafed species of the Japanese butterbur. In Japan, the plant is called “fuki" with chefs sometimes using its parts as a condiment or in the preparation of sushi. Japanese children find that the long stems and large leaves make perfect umbrellas.

Hardy from Zones 5-8, P.j. var. giganteus bears round leaves about 3-4 feet in circumference supported by tall stems. It flowers early with aster-like white blooms, but I find the blooms rather insignificant compared to its large leaves.

Requirements for growing the plant are very specific...plenty of room, shade and a moist environment. These were exactly the conditions in a space seen from the little footbridge bordering one side of our brook. Skunk-cabbage originally occupied this place, a native that never wins blue ribbons at a flower show, but the petasites foliage is spectacular. Before you rush out to plant, make sure that there is plenty of spread room without encroachment upon valuable vegetation.

If your situation is not quite as damp, or you're worried about any plant that can sometimes become invasive, try P.j. 'Variegatus' which has yellow to white blotches of coloring. For me, it has grown much slower than giganteus, but each leaf is only 24 inches across. And then, too, it needs a bit more sun to bring out those colors.

A recently introduced plant from Oregon, Petasites frigidus var. palmatus 'Golden Palms' is a wild western sport with foot long leaves that should take a bit more sun in our area. It is described by its introducer, Terra Nova Nurseries, as having “metallic golden palms" and is said to be hardy only to Zone 6. Like other petasites, it needs constantly moist soil. Given plenty of room to spread, all these petasites will create that surprise you're seeking.

If none of the above fits your situation, then another way of introducing big leaves to your garden is by pot growing or temporarily using tropical plants in beds.

Try those in the aroid (arum) family. The most notable are Alocasias, Colocasias, and Xanthosomas, all referred to as Elephant's Ears. They are also called “taro," but colocasia is the species usually grown commercially for its edible tubers. A typical “large" arum has leaves 3-4 feet broad completely covering its tall stems. However, when young, arums might not be so exuberant. Although tender in the Northeast, it is not difficult to hold them over during the cold season. Dig and store the tubers in the winter or keep potted plants growing in a warm, sunny window. I place the pots in my cool (55-degree night temperature) greenhouse where they sport large leaves until January at which time some turn brown and drop. No need to fret. Growth resumes in spring. It may take quite a few years to produce maximum sized leaf growth so up-potting is advisable at the start of each growing season plus the addition of adequate fertilizer. Their culture is pretty much the same. Alocasias and colocasias are quite difficult to tell apart but generally, the alocasias have firm, upright leaves while the colocasias tend to have downward leaning foliage that is a bit floppier.