Do the Math: Divide and multiply your perennials

Perennials have much to offer gardeners. Many, such as black-eyed Susans, ornamental grasses, daylilies, hostas and ferns, are long-lived, returning every year to add color and texture to beds and borders. At some point, however, these plants and others may need to be lifted out of the ground and divided. Many plants can be divided in late summer, but spring is a great time for this task because they then have the entire growing season to recover and produce a sturdy new root system.

Dividing perennials is beneficial for several reasons. It helps rejuvenate plants such as Siberian irises, which produce large clumps of leaves. Dividing is used to control aggressive, spreading perennials, such as yarrow (achillea) and monarda. It’s also an easy way to increase plants for your garden. 

Handy tools for dividing plants include a spade with a sharp edge, a gardening fork, and, my favorite, an old bread knife with a serrated blade. After planting the new divisions, water them with a diluted liquid transplant solution, such as Miracle Gro’s Quick Start. These products promote root growth. 

Divide and multiply

Hostas are among the easiest plants to divide in spring. When the leaves are a few inches tall, use a fork or a spade and dig up the entire clump. Brush or wash away the soil so you can see where the clusters of fleshy roots join the leaves. Each cluster is a separate plant. Carefully tease the individuals apart, so that each one has a few leaves and a good clump of roots. Set the new divisions in the ground at the same depth at which they had been growing and water thoroughly. This method works on daylilies, pulmonaria, coneflowers, and other clump-forming perennials. 

Donut hole, anyone? 

After a few years in the garden, ornamental grasses, such as fountain grass (Pennisetum), Japanese silver grass (Miscanthus), and switchgrass (Panicum), develop a dead spot in the center of the clump. Marcy Stewart-Pyziak of The Gardener’s Tutor in Manhattan, Illinois, calls this a donut hole.  “The plant grows in a ring, and the inside is basically dead,” Pyziak said. “The same thing often happens to Siberian iris. When it does that, you know it’s time to divide the plants.” And divide you must, otherwise the grasses become floppy and the Siberian irises produces fewer, smaller flowers. 

For Siberian irises, dig up the entire plant with a fork or spade and set the clump on a tarp or the ground. This is where an old bread knife or a small handsaw, set aside just for this purpose, can cut through the emerging leaves and rhizomes (thick underground stems that produce the shoots and root systems of new plants). Each division should have a hefty rhizome or two. Discard any woody parts and replant. Siberian irises (and other types of iris) benefit from division every three years or so. As with the hostas, set the plants back in the ground at the same depth they were growing, add compost or other organic material, and water them well.  You can do the same thing for bearded irises (shown at left).

When it comes to rejuvenating large ornamental grasses, they are usually too big to dig out of the ground. And, most ornamental grasses do not produce green leaves until early May. But in March, I use long-handled hedge shears to cut the old leaves as close to the ground as possible. That’s the easiest way to see the “donut” that has developed--the inside of the clump is usually soil or debris. Next, I use a sharp spade and slice a few sections from the outside of the “donut.”  I dig up these sections (even though there are no green leaves yet) and move them elsewhere in the garden or toss them in the compost. Some, like Morning Light Miscanthus, I plant in large containers with annuals. 

Divide and conquer

Some runaway perennials, like asters, yarrow, helianthus (summer sunflower) and monarda spread by underground runners and may need dividing every year to keep the plants healthy and prevent them from running wild. When the leaves are just a few inches tall in spring, it’s easiest to slice a few sections with a spade, lift them out of the ground, and use them elsewhere or compost them. This technique also works on coreopsis, epimedium, lysimachia, lily-of-the-valley, bishop’s weed, and sweet woodruff (Galium). 

If you didn't get around to dividing your perennials this spring, you can do it in late summer. A good rule of thumb is to get the divisions back in the ground by September 15 so they have a month to get their roots established before the first hard frosts hit the area.  As with any transplants, keep them watered, especially during dry periods.

Here’s a general guide to some common garden perennials and the best time to divide them.

Plant Spring        Aug/Sept

Achillea                   X           X

Carex (sedge)         X

Chrysanthemum     X

Coneflower             X           X

Coreopsis               X

Epimedium             X           X

Ferns                      X

Helianthus              X

Hemerocallis           X          X

Heuchera                X          X

Hosta                      X          X

   

Iris                           X          X

Ornamental Grass    X

Pulmonaria            X          X

Summer Sowings: Swiss Chard it is!

'Bright Lights' Swiss Chard in resin pot

There’s still plenty of time to plant two delicious greens--Swiss chard (Beta vulgaris) and Bok Choy (Brassica rapa)--for a prolonged harvest. Both are easy-to-grow, nutritious veggies that do very well in cool weather.  Gardeners often sow them in the early spring and again in July and August for a fall harvest. 

Whether you sow them now from seeds, or buy transplants from your local garden center, Swiss chard and Bok choy should be planted in fertile, evenly moist soil that receives full sun.

“Bok choy is one of the easiest and fastest vegetables to grow,” says Renee Shepherd, owner of Renee’s Garden (www.reneesgarden.com), a mail-order seed company. “It grows well in cool spring weather and you can also definitely plant another crop again at the end of the summer for late fall harvest.”

Bok choy (aka Bok choi, Pak choy or Pac choi) is a vigorous, fast-growing Asian green that provides a good source of calcium, fiber and vitamins A and C. Plants tend to be vase-shaped with thick white stalks. In fact, the name means “white vegetable” in Chinese. The flavor might best be described as tangy-sweet yet delicate. It can be used in stir-fries or as baby salad greens when the plants are 2 to 3 inches tall.  

When sowing Bok choy seeds, plant them about 1/4 inch deep and 2 inches apart.  Seeds sprout in about 5 to 7 days and harvesting begins in about 35 days. “Bok choy just needs fertile, well-drained soil and it's important to thin the young seedlings to stand about 5 to 6 inches apart so they have room to make pretty vase-shaped plants of crunchy pastel green stalks and deep green leaves,” Renee Shepherd says.  When planting from transplants, set the plants in at 5 to 6 inches apart.

When bok choy plants are small, you can cut a few baby leaves from each one and use them raw in salads.  Some cultivars, like ‘Red Choi,’ have attractive leaves that change from dark green with maroon veins when they’re tiny to dark maroon leaves that are green underneath when they mature. Depending on the cultivar, Bok choy grows between 10 and 15 inches tall. 

Swiss chard is another versatile vegetable. It can be sauteed whole when the plant is small and it’s a great substitute for spinach. You can add the sliced leaves or ribs to soups and chowders or saute the leaves with other greens. The All-America Selection ‘Bright Lights’ is particularly ornamental with fleshy stalks in shades of pink, white, red, gold, coral and yellow.  For maximum color in the stems and leaf veins, the leaves of ‘Bright Lights’ should be at least 8 inches long when harvesting. 

Plant Swiss chard seeds 1/2 inch deep and 2 inches apart. Thin out the extra seedlings and use them as early greens. The final spacing between plants should be 12 to 18 inches apart. Harvest plants when they have 6 to 8 stalks. Leaf miners, insects that tunnel into tender leaves, can be a pest. Remove spoiled leaves and wait for new growth. 

Chard should be harvested as needed because its high water content means that it won’t store for long in the refrigerator.  For baby greens, sow seeds 2 inches apart and harvest when they are 2 to 3 inches tall.  Harvest mature chard when it’s about 10 inches tall.  Cut off the outer leaves, and the plants will keep producing even through a light frost.  

Renee Shepherd shares her bok choy and chard recipes from her books, “Recipes From a Kitchen Garden,” and “More Recipes from a Kitchen Garden” available at www.reneesgarden.com and at the Morton Arboretum gift shop in Lisle. 

Milanese-Style Chard

1 bunch (1 pound) Swiss chard

2 T olive oil

1 clove garlic, minced

6 scallions, thinly sliced

2 T chopped fresh parsley

1/4 cup chopped fresh basil

Pinch of nutmeg

1/4 cup chopped prosciutto or ham

2 T freshly grated Parmesan cheese

Salt and freshly ground pepper to taste

Garnish:  2 T toasted pine nuts or chopped walnuts

Trim the chard, discard tough stems and coarsely chop. In a large, deep skillet, heat olive oil, add garlic and scallions and saute until softened and fragrant, 2 to 3 minutes. Add chard, parsley, basil, nutmeg, prosciutto or ham, and mix well together. Cover the skillet and cook over medium heat until tender and wilted, 3 to 5 minutes. Mix in Parmesan cheese. Add salt and pepper to taste. Garnish with nuts. Serves 4 to 6.  

Orzo, Chard and Squash Casserole

1 1/2 cups orzo (rice-shaped pasta)

1 T butter

1/4 cup chopped fresh green basil 

1/2 cup grated Muenster cheese

Freshly ground pepper to taste

1 T olive oil

2 medium zucchini, quartered lengthwise, cut into 1/4-inch slices

2 1/2 cups sliced mushrooms

10 large leaves of steamed chard, coarsely chopped and drained

2 cloves of garlic, minced

1 T drained capers

Salt to taste

Freshly grated Parmesan cheese

Bring a large pot of lightly salted water to a boil. Add orzo and reduce heat, cooking until orzo is tender, about 10 to 12 minutes. Drain, add butter, basil, Muenster cheese and freshly ground pepper. Set aside. In a large skillet, heat oil, add zucchini and mushrooms and saute until almost tender, stirring frequently for 3 to 5 minutes. Add chopped chard and garlic. Continue cooking, stirring frequently until zucchini is soft.  Stir in capers. Toss vegetables with orzo and add salt to taste. Sprinkle with Parmesan cheese.