Vegetable Feast: Sweet Potatoes, Walking Onions, and Water Timers

In his “Vegetable Feast” column, horticulturist Frank Hyman offers seasonal gardening advice paired with his own trademark wit.

Sweet Potatoes: Sweetheart of the Summer Garden

Both white potatoes and sweet potatoes are delicious, but sweet potatoes can be better for you: their orange flesh offers beta-carotene, fiber, and B vitamins, and they’re lower on the glycemic index. Some sweet potatoes have been bred to have white, yellow, or purple flesh. The young leaves are tender, tasty, and nutritious enough to eat like sautéed spinach all summer long.

Sweet potato transplants (called slips because, when they are about 8 inches long, these shoots “slip” right off the potatoes) show up at garden centers in late spring. They often come in a bundle of 50 with tiny, inadequate-looking roots or sometimes no roots at all. But at any stage, a sweet potato (Ipomoea batatas) is about the toughest plant in the vegetable garden, so don’t worry about the roots—they’ll do fine.

You can also grow your own slips by sprouting a sweet potato from last year’s harvest or even an organic sweet potato from the farmer’s market. (Conventional sweet potatoes are often sprayed with a chemical called BudNip to prevent them from sprouting.) Cut the potato in half lengthwise, lay it on a bed of moist sand, and put it on a sunny windowsill. In about three weeks, you’ll have slips sprouting from the sides of the potato.

Here is your chance to teach kids about cloning. A clone is any new plant with DNA that’s identical to its parent. Plants propagated by cuttings, divisions, or in this case, sprouts, are all clones. On the other hand, plants propagated from seeds get half their DNA from each of their two parents, as humans do.

With your slips collected and your bed freshly turned, drop the slips on the ground about 12 inches apart in the row, in rows that are also about 12 inches apart. Use a tool like a broom or rake handle turned upside down. From a standing position, use the tip of the handle to push the bottom end of the slip into the soft ground until only the top leaves are showing. A 2-by-2 stick will also work. This is a good use for worn-out tools: cut off the worn-out end and save the long handle to use as a garden stake or for poking sweet potato slips into the ground. As each slip is poked into place, use the tip of your toe to settle the soil around the root. When you’re done planting, give each slip a shot of water.

Giving children these tasks could be a good lesson in teamwork: one kid drops the plants on the ground, another pokes them with a stick (this will be a popular job), the next one settles the soil with their toe, and the last one pours some water on each plant. Adults also appreciate this technique since it requires no bending over.

Outside of long droughts or desert conditions, no summer irrigation is necessary for sweet potatoes—they are that tough. Sweet potatoes do like it hot, so northern gardeners may want to use black plastic mulch, which heats up the soil. But because they spread across the ground quickly, shading the soil, suppressing most weeds and outrunning the rest, some gardeners even forgo mulch. Sweet potatoes are also generally free of insects and diseases, making them a great cost-effective crop that won’t need babysitting all summer.

Harvest some or all of the potatoes any time after Labor Day. Cut the leafy vines to the ground first and feed them to the chickens or the compost bin.

Dig the potatoes with a shovel. A range of sizes will be found on the roots of every plant. If you have warm, dry, fall weather, leave the potatoes on the ground for a few days so the skins dry out enough to be stored indoors for several weeks or months. Ideally, save one or two to start slips next spring.

To cook them, pierce the skins with a fork and bake for 45 minutes at 400°F for a sweet, moist, nutritious side dish that really doesn’t need butter or spices.  

Save Time and Water with a Water-Timer

Occasionally I see gardeners struggling to keep their gardens watered by hand. Most hoses might put out about 10 gallons per minute. For an urban gardener in an older part of town, corrosion in the water pipes may cut that rate in half.

To grow well in summer, a vegetable garden needs—very roughly—a gallon of water per square foot per week, if there’s no rain. So watering about 600 square feet of garden would take one to two hours of your time every week if done by hand. And there’s still the rest of the garden to tend to.

But there’s an alternative that I rely on: inexpensive timers mounted on the spigot allow the right amount of water to run through a soaker hose or sprinkler and then they shut off the water for you.

I know timers work because I set up all my garden clients with them. Since 99 percent of my clients aren’t gardeners, the timers let me create a simple push-button irrigation system that allows non-gardeners to keep new plants alive.

These timers work the same way an egg timer does in the kitchen. Turn the dial to a set amount of time and tick, tick, tick, it works its way through a countdown and turns off the water on schedule. They cost $10 to $15 and are available at most garden centers.

It’s this easy: 1) screw the timer onto the spigot, 2) screw the garden hose onto the bottom of the timer, and then 3) connect the garden hose to a soaker hose or sprinkler in the garden. Remove the timer in winter so ice won’t crack it open.

Then do as I suggest to my clients: turn on the timer on your way out of the house. You can be confident that the watering will stop while you’re away. You might leave the house with the nagging feeling you’ve left the oven on—I can’t help you there—but you won’t come home to find your yard a swamp.

When you do arrive home, move the garden hose to water another bed and set the timer again before you go in to make dinner. No standing around required.

Self-Starters: Egyptian Walking Onions

I try to save time in the garden, and what could save more time than for vegetables to replant themselves every year? All we would have to do is keep them mulched and gather the harvest. Am I just dreaming?

Most popular vegetables—tomatoes, broccoli, etc.—are annuals and only live for a few months before dying. That’s why we have to resurrect the vegetable garden each season. But a few vegetables are perennials, meaning they live year after year. You’re probably already familiar with perennial veggies like asparagus and rhubarb that come back every spring. Another perennial vegetable is Egyptian walking onion. These onions are delicious, drought hardy, and pest free, and they keep multiplying—on their own.

Walking onions (nobody really knows if they’re from Egypt) don’t set seed at all. In early summer, odd-looking clusters of four to eight bulblets erupt at the top of their 2-foot-tall, pillar-like green leaves. If you’re familiar with pearl onions, you’ve got a good idea of their size and range of color. Called topsets, these thumb-size bulbs get heavier until mid- or late summer, when their weight causes the leaves to arch to the ground. Left alone, the topsets will root where they land. That’s why they’re called walking onions (although their pace is more of a saunter).

Once set in, or on the ground, the rooted topsets grow into 2-inch-wide onions. They send up fresh leaves and grow new topsets the following summer, which then take another slow step on their perennial journey.

You can harvest walking onions at one or more stages:

1) Year-round, you can eat the greens and use as you would chives or spring onion greens.

2) From fall to spring, harvest some of the small, first-year onions from the ground as scallions. Any remaining bulbs will keep growing and multiplying.

3) In midsummer, harvest some of the full-size bulbs.

4) Also in midsummer, harvest the mature topsets. Though small, like pearl onions, they are super-easy to peel if you boil them for a minute or two, drain, dunk in an ice bath, cut the root end off, then squeeze ‘em till they pop out of their skins like a muscadine grape. (StartCooking.com/blog/202/How-to-Peel-Pearl-Onions)

Do leave some bulbs unharvested in a dedicated bed so they can save you time by creating next season’s crop. Or harvest and poke bulblets about a finger-joint-deep into moderately fertile, prepared soil to help them kick off their promenade.

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