No other plant species can rival the diversity of vegetable garden forms found within the cabbage species, Brassica oleracea, which includes cabbages and cauliflower, kale and kohlrabi, Brussels sprouts and broccoli. Since we grow all of these biennials as annuals, we never see the flowers or we would not be surprised by this lumping; in bloom, they all look pretty much alike.

What is this kohlrabi? I’m sure some of you have grown it, but most, particularly those new to vegetable gardening, have little or no knowledge of this member of the group. Well, think of kohlrabi as a mutant form of broccoli that has given up any idea of flowering in the year it is planted and, instead, decides to put all of its energy into production of an enlarged bulblike lower stem from which the leaves grow. At harvest, when the bulbous stem is cut at ground level and the leaf stalks removed, what you hold in your hand looks like a Sputnik yanked out of orbit.

I first tasted kohlrabi more than 30 years ago, my first year as horticulturist-in-training at Park Seed Co. in South Carolina, walking down the cabbage row of the field trials with George Park. He plucked a small kohlrabi from the ground, peeled the skin with a pocket knife, and handed it to me like an apple.

“Take a bite,” he commanded.

Being in the cabbages, I was not sure that I really wanted to follow orders, and took just a nibble. It was delicious! He picked and peeled his own, and we crunched kohlrabi down the row like two mules crunching carrots.

I recall the sweetness and apple-crispness, but also a spicy tang, like water chestnuts. I have since learned what George knew, that the best kohlrabi is harvested when the stems have enlarged to no more than 2 inches in diameter. As they get larger, they get woodier and lose their sweetness.

I have not grown kohlrabi since leaving that job, but things are about to change. Each year I like to experiment with something new, and I am declaring 2010 as the Year of Kohlrabi in Marjorie’s Garden.

I want to try as many varieties as possible in this great experiment and, realizing that kohlrabi does not store for long periods of time after harvest, plan to make numerous small sowings starting in early spring and continuing through the summer. If the summer turns hot, I may lose some sowings, but late-summer sowings will provide a fall harvest.

Rapid growth makes for the best eating. I plan to dig in a generous amount of finished compost wherever I sow kohlrabi seed.

As for varieties, there are too many to mention in this space, but my selection criteria include color, size and taste. Yes, you can get kohlrabi in either purple- or green-skinned varieties. In its online catalog (www.reneesgarden.com), Renee’s Garden offers a new variety, Crispy Colors Duo, a mix of the purple and green. I can imagine a small planting just before harvest, the color it would add to the garden.

There are a few varieties that supposedly grow stems to 8 or 10 inches in diameter without getting woody and losing their flavor. I plan to try just one, the variety Kossack offered by Johnny’s Selected Seeds of Winslow (johnnyseeds.com). The catalog promises it will keep in storage for up to four months.

I think of kohlrabi as a vegetable to be eaten raw, diced into salads and stir-fries. But I read that it also can be cooked, like a turnip. I will leave it to my experienced readers for other suggestions on how to enjoy this unusual vegetable. Send me your favorite recipe and I will share it with all.

For a few recipes along with more information about kohlrabi, visit Renee’s Garden spotlight on kohlrabi at www.reneesgarden.com/articles/kohlrabi.html.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@shead.org. Include name, address and telephone number.