Plant Information

Plant Information

May Checklist

The Value of Native Plants

Stroll through the Garden’s 100-acre McDonald Woods this month and you'll be greeted by countless trees and shrubs unfurling their flower buds and leaves. Underneath them, small but spectacular wildflowers continue to bloom and bees (and the occasional hummingbird) are buzzing around collecting nectar and pollen. 

Marsh marigolds, swamp buttercups, trillium, Dutchman’s breeches, anemones, shooting stars and many other delicate spring ephemerals flower before the trees fully leaf out. They take advantage of the sunlight that reaches the forest floor before the overhead canopy casts an umbrella of shade come May. These wildflowers were among the original flora that once blanketed thousands of woodland acres across northeastern Illinois.

Shooting stars

Shooting Stars

Although they are extremely attractive, they are underused in many home gardens.  We’d like to change that because native plants are truly unique. They have successfully grown and evolved over thousands of years, adapting to the soils, insects, fluctuating seasonal rainfall, freezing winters, and hot, humid, summers. 

Plants that grew in this area before settlers arrived were the cornerstone in a sustainable web of life. They support native insects, birds, mammals and infinitesimally tiny soil organisms—all of which evolved with the plants. (One well-known example is the monarch butterfly, which only lays its eggs on milkweed (Asclepias) species. The caterpillars are among a handful of insects that can ingest chemicals from the plant, which makes them distasteful to predators. It’s a unique plant-insect relationship that developed over millennia.)

There’s a multitude of benefits when you add a few native plants to your garden. They can offer food, shelter, nesting material, and a place for insects and birds to lay their eggs. They tolerate the vagaries of an ever-changing climate. If urban, suburban and rural homeowners planted attractive natives on their property, their efforts would go a long way to supporting wildlife and providing enjoyment. After all, who doesn’t like watching birds and butterflies in the garden? 

Native Plants and Birds

According to a recent study by the Cornell Lab of Ornithology, bird populations have declined by nearly three billion since 1970, a number that scientists have called staggering. The reasons for the decline are numerous, but habitat loss and the resulting lack of food plays a significant role. That’s because many birds feed insects (not seeds) to their young. Those insects have evolved to make use of native plants. However, native insects have not evolved to take advantage of non-native plants, such as Bradford pears or rhododendrons. A lack of insects—especially caterpillars—means little or no food for hatchlings. Adult birds must spend energy flying longer distances from the nest looking for suitable food. 

As Doug Tallamy writes in his book, “Nature’s Best Hope,” (Timber Press, 2019), “To realize the ecological potential of our landscapes, most of us have to increase the abundance and diversity of our plantings.” That means adding to our plant palette at home with trees, shrubs, vines and perennials that once grew long ago where we now garden. 

Sedum ternatum

Sedum ternatum

A Shade-loving Sedum

There are many beautiful sedums that are pretty in the garden and attract some butterflies, but most are not native to the United States. However, there is a native woodland sedum, aka wild stonecrop—Sedum ternatum. It is the only sedum species native to central and northern Illinois. A miner bee visits the sedum flowers for nectar and pollen. These solitary bees have lives that evolved to correspond with the bloom time of specific wildflowers, such as wild stonecrop. While most ornamental sedums grow in full sun, this one is normally found in or near woodlands. It makes a perfect addition to the shade garden where it provides spring blooms, attractive foliage and supports native wildlife.

When you’re plant shopping this spring, consider adding some beneficial native species to your garden beds and borders. The birds, bees and other critters will thank you.

 

The Woodland Garden

Dutchman's Breeches

The following native perennials make great partners for existing hostas, hellebores or epimedium (barrenwort) in the shade garden. Some species may be more challenging to find so look for local native plant sales, independent garden centers and online. 

Actaea pachypoda (doll’s eyes)
Aquilegia canadensis (wild columbine)
Anemonella thalictroides (rue anemone)
Asarum canadense (wild ginger)
Arisaema triphyllum (Jack-in-the-Pulpit)
Adiantum pedatum (maidenhair fern)
Amsonia tabernaemontana (bluestar)
Athyrium filixfemina (lady fern)
Cimicifuga racemosa (black cohosh)
Claytonia virginica (spring beauty)
Dicentra cucullaria (Dutchman's breeches)
Dryopteris spp. (wood ferns)
Erythronium (trout lily)
Geranium maculatum (wild geranium)
Gillenia trifoliata (Bowman’s root)
Mertensia virginica (Virginia bluebells)
Polemonium reptans (Jacob's ladder)
Polygonatum commutatum (Solomon's seal)
Polystichum acrostichoides (Christmas fern)
Sanguinaria canadensis (bloodroot)
Sedum ternatum (wild stonecrop)
Uvularia grandiflora (large-flowered bellwort)

The Sunny Border

Litaris

Amorpha canescens (leadplant)
Andropogon gerardii (big blue stem)
Asclepias incarnata (swamp milkweed)
Baptisia (wild indigo)
Camassia scilloides (wild hyacinth)
Coreopsis lanceolata (lance-leaf coreopsis)
Dalea purpurea (purple prairie clover)
Eryngium yuccifolium (rattlesnake master)
Eutrochium maculatum (spotted Joe Pye weed)
Filipendula rubra (queen-of-the-prairie)
Helenium autumnale (common sneezeweed)
Liatris (blazing star)
Monarda (beebalm, bergamot)
Oenothera pilosella (prairie sundrops)
Parthenium integrifolium (wild quinine)
Phlox pilosa (prairie phlox)
Physostegia virginiana (obedient plant)
Ratibida pinnata (yellow coneflower)
Rudbeckia triloba (brown-eyed Susan)
Schizachyrium scoparium (little bluestem)
Silphium laciniatum (compass plant)


Nina Koziol is a garden writer and horticulturist who lives and gardens in Palos Park, Illinois.

May

General Garden Care

General Garden Care

Plant warm-season flowering annuals, vines, herbs, and vegetables after the Chicago area’s average last frost date of May 15. Cautious gardeners often wait until Memorial Day before setting out cold-sensitive plants such as tomatoes, peppers, eggplants, and squash. Pinch back one-third of new growth to encourage stocky habit (except vines). Be sure newly purchased annuals have been hardened off properly before planting them outside. Avoid fertilizing newly planted annuals for two weeks.

Continue to plant new perennials, ornamental grasses, and roses in containers. If plant roots are root-bound (encircling the pot), make four cuts into the bottom of the root ball with a sharp tool, and flare the sections outward when planting.

Provide a gentle water drip for migrating birds. The May migrants — warblers, tanagers, orioles and buntings — are all attracted to shallow pools and the slight pinging sound of dripping water.

May

Annual and Perennial Care

Peony

Stake tall perennials before they reach 6 inches. Begin to regularly pinch back fall-blooming perennials such as chrysanthemums, asters and tall sedums. Pinch once a week until the middle of July. This promotes stocky growth.

Continue to direct the growth of perennial vines on their supports. Climbing roses should be encouraged to develop lateral, flower-bearing canes.

Continue to check peonies for botrytis blight or other foliar fungal problems. Peonies that suffered from botrytis or bud blast last year should be sprayed regularly, starting when the plants are between 2 to 4 inches tall. Cage or provide support for peony blossoms when the plants are 10 inches tall.

Let spring bulb foliage yellow and wither before removing it. The leaves manufacture food that is stored in the bulb for next year’s growth. Even braiding the foliage of daffodils can reduce the food production of the leaves.

Spray emerging lily shoots with antirodent spray if rabbits and deer have been a problem. Be sure to reapply after rainfall.

Monitor all annual plantings in window boxes and containers. On warm, windy days, hanging baskets will require water every day. Always water the soil thoroughly before adding dilute quarter-strength fertilizer to containers. Terra cotta pots will dry out faster than plastic. Consider incorporating water-conserving granules into container soil.

Plant tender water lilies and lotus when the water temperature is over 65 degrees.

Plant summer- and fall-flowering bulbs such as Asiatic and Oriental lilies, dahlias, peacock orchids (Acidanthera), cannas, tuberous begonias, caladium, crocosmia, freesia, gladioli, montbretia, and calla lilies.

May

Tree and Shrub Care

Lilac

Trees and shrubs, including balled and burlapped evergreens, can still be planted this month. Plant on a cloudy day, early in the morning, to prevent heat and transplant shock. Water thoroughly and gently at planting time and continue for the first year with 1 inch of water a week, spread throughout the root zone. Mulch root zones to conserve moisture.

Prune spring-flowering shrubs and ornamental trees immediately after they bloom. These include forsythia, viburnum, lilac, small magnolias, rhododendrons, and azaleas. Prune to the ground old canes of forsythia and lilac. Alternative time to do renovation pruning is in late winter when plants are dormant. Deadhead (or lightly prune) spent lilac blossoms to increase flower production. Avoid fertilizer with excessive nitrogen; it can encourage foliage at the expense of flower production.

Lilac blossoms will last longer indoors if they are cut in the morning on a long woody stem when the flower is only half open. Cut a second time indoors before putting in a vase and make a vertical slit up the woody tissue.

Gently pull off dried flowers of azaleas and rhododendrons. New sticky shoots are located at the base of these flower trusses. Take care not to break these shoots when removing flowers. To increase flower production for the following year, pinch off one-half of this new green growth when it is at least one inch in length.

May

Rose Care

rose bud

Fertilize roses with a liquid 20-20-20 solution when flower buds are set.

Monitor roses for insects and diseases. Check daily for black spot, especially in wet weather. Do not handle rosebushes if foliage is wet and infected. Wait until leaves have dried before removing them and spraying.

Monitor roses for rose slugs (small white caterpillars with black heads) and their damage (tissuelike patches on the leaves).

Succulent new green growth is particularly susceptible to aphid attack. Monitor newly planted shrubs, small flowering trees, and juicy perennials for signs of aphids — curled, distorted tip growth. Spray a strong stream of water on damaged foliage to remove pests.

May

Lawn Care

Lawn Care

Mow lawn at 2 to 2½ inches, removing one-third or less of the leaf blade. Leave grass clippings on the lawn to return nutrients to the soil, or add them to compost heap. Rake clippings slightly if they are heavy and wet. If you are applying grass seed, do not use a pre-emergent weed killer in the same area.

Fertilize lawn in mid-May if necessary. Late fall is a preferable time to fertilize. Monitor for weeds and hand pull or spot treat accordingly.

May

Fruit, Vegetable, and Herb Care

strawberries

Plant corn, snap beans, summer squash, and New Zealand spinach in mid-May.

Thin carrots, beets, and late lettuce.

Harvest green onions, lettuce, and radishes. Any of the mesclun mix or cut-and-come-again lettuces can be harvested to a few inches three separate times before the plants have exhausted themselves.

Harvest mature asparagus and rhubarb.

Spread several inches of aged compost on vegetable and herb beds, if not done yet.

Remove flowers of June-bearing strawberries as soon as they appear. This is necessary just for the first growing season. The plants will now develop a stronger root system.

Remove flowers for everbearing and day-neutral strawberries as soon as they appear. Flowers that develop after July 1 can be left on the plants to set fruit for later in the season.

May

Indoor Plant Care

geranium

Begin to harden off warm-season transplants, moving them into a cold frame or protected area.

Gradually move houseplants outside to protected areas. Large houseplants in plastic pots should be slipped into larger heavier pots to prevent them from falling over in wind. Guard against overexposure to afternoon sun. Carefully monitor for insects during their time spent in the garden.

Overwintered tender annuals or tropicals (e.g., hibiscus, gardenia, geranium) may be pruned, fertilized, and taken outside once night temperatures reach 40 degrees.

Amaryllis bulbs (in their pots) can be moved to a protected spot in the garden where they receive morning sun. Fertilize twice a month with a dilute 15-30-15 mix.

May