GARDENING : Forcing Summer Plants Into Winter Duty

Have you ever heard of petunias being grown as perennials? One gardener tells how every fall she digs up a petunia plant, pots it up to keep it blooming indoors through the winter, then plants it out again each summer (still blooming). What gardeners will do to preserve a bit of summer’s garden.

In midwinter, sunny window space is at a premium, best devoted to a few flowers and perhaps pots of basil, chives and rosemary. Is there anything (besides mushrooms) that can be grown in little light? Or even no light? The answer is yes, and the plants are vegetables, or at least certain vegetables.

Old English gardening books mention vegetable “forcing,” which means growing vegetables out of season. Certain vegetables are best forced in the dark.

These are leafy vegetables which, when grown in the light, have flavors that are just too robust, usually sour or bitter. But grown in the dark, these vegetables take on a delicate flavor and tender succulence.

Rhubarb, sea kale and Belgian endive all make thick storage roots when grown outdoors. If pieces of their roots are dug up and potted, they will re-sprout shoots even in the dark.

A couple of years are needed before perennials like rhubarb and sea kale develop sturdy enough root systems so that a portion can be sacrificed to dig for forcing. Of course, if a rhubarb plant is getting old and needs division, this is an ideal time to garner a few pieces of roots for repotting.

Sea kale is a popular forcing vegetable in England. When properly grown, it tastes somewhat like hazelnuts, with only a slight bitterness. (Sea kale is not to be confused with the “sea kale beet” of English gardening books, which is the Queen’s English for our Swiss chard).

Belgian endives, those torpedo-shaped, pale-green leafy heads that sell for a small fortune in grocery stores, are grown as annuals. Seeds sown in early summer make roots large enough by now for forcing.

Vegetables forced in the dark are sustained by the energy stored in their roots, so the potting soil needs to supply only moisture and air to the roots.

And because they only spend a short while in the pots (soon depleting their energy reserves), you can set the root pieces close to each other.

So dig up some set root pieces and set them top-sides up and an inch or two apart in flowerpots or boxes filled with sand, old potting soil, new potting soil, or anything else that will provide moisture and aeration for the roots.

After potting, either place the pots or boxes in darkness or cover the root crowns with inverted flowerpots.

Almost any vegetable whose flavor is improved by blanching in the dark can be forced indoors. Others might include cardoon, a perennial that tastes like artichoke, and finocchio, a celery-like plant with a taste of anise.

Curly endive usually is blanched right out in the garden, but you can dig up the plants and force them indoors. Dandelion is a closely related plant that can be treated similarly.

With an adequate supply of roots, some can be potted and left outside or in a garage, where the cold will delay their growth. Bring indoors a few at a time, as needed, for forcing.

How fast they grow indoors depends on how much warmth you give them. By staggering their growth, you can have a supply of fresh, albeit pale, greens through the winter.