Bob Lilly talks about gardening on a houseboat

Bob Lily gardens on water. This Seattle horticulturalist, plantsman, and designer extraordinaire has lived on a houseboat in Lake Union, since the 1970s. His shake-shingled dwelling disappears under a cascade of greenery—with everything grown in containers. And his diverse plant collections also adorn six other nearby houseboats. This month, I asked him for ideas and advice about gardening in pots.

Overwintering on Water – I had assumed the moderating lake temperature would protect his plants through the winter. Not quite. “I do have stuff die that would have lived on land,” says Bob, “because the containers aren’t standing on the ground where they would benefit from a cone of warmth.”

Although Seattle has relatively mild winters (Zone 8b), it can still receive what local forecasters call, “Canadian blasts.” But some plants have frozen solid and made it through, Bob tells me, including pines and junipers—no surprise there—but also sempervivum, wisteria, and upright rosemary. “Rosemary ages poorly in pots, but it will live as long as it has adequate water,” he notes. “There’s nothing quite so dead as a bone-dry rosemary.”

Watering – The traditional method for watering plants on a houseboat? “Dip a bucket in the lake, or use a saucepan, tied to a long handle,” Bob says. He delivers an inch of water onto the surface of each pot.

Starting from Seed – Bob likes to conserve heritage open-pollinated varieties by growing them in his container gardens. As President of the Hardy Plant Society of Washington, he contributes to their yearly seed exchange. With no greenhouse on the dock, he starts many plants for his group’s sales in a member’s on-shore facility.

Naming his Favorites – Bob likes tall and dramatic. “Pole beans are so much fun to grow,” he says. Six-foot bamboo stakes support the Italian red-splashed shell bean, Tongue of Fire ( Borlotto Lingua do Fuoco), and the purple pole bean (Trionfo Violetto). “And I love growing kiss-me-over-the-garden-gate (Persicaria orientalis),” says Bob. “They flower late and get ten feet tall in eighteen-inch diameter pots.”

Bob’s top favorite plants—wouldn’t you know?—are lilies. All kinds, except martagons. “Don’t try martagons in pots,” he says. “They just won’t grow.” But the new orienpet hybrids, like six-foot Lilium ‘Scheherazade’ and ‘Silk Road’, are great candidates for containers. And they are happy there for years. “I had eight to ten ‘Uchida’(L. speciosum var.‘Uchida’) in a large wooden pot for sixteen years,” Bob says. “When I took it apart, there were at least fifty bulbs in it.”