Q: I would like to plant some peonies in my garden. Can I do it in the fall, and what tips can you offer?

A: Yes, peonies can be planted and divided in the fall. Peonies are favorites for many people because they are long-lived, hardy perennials that reliably produce gorgeous, often fragrant flowers in spring. Select a full sun location for best flowering. Peony roots should contain three to five red eyes and be planted no more than 2 inches below soil level in a humus-rich, well-drained soil. Choose and prepare a site carefully so that, once established, peonies can remain undisturbed for many years.

Q. I have an established planting of peony bushes that are attacked by blight every year. What is the best way to prevent this disease from recurring?

A. Peonies can suffer from several fungal blight problems, including botrytis and bud blast. The leaves and stems develop dark spots or streaks, and the flower buds turn black and never open. These fungal problems favor damp, crowded conditions where there is inadequate sun and air circulation. Always plant peonies in full sun in soil with good drainage. If the fungus persists, they will need to be sprayed annually with an approved fungicide as soon as the shoots are 2 to 4 inches tall in early spring. Repeat the spraying as per label directions. Infected foliage must be removed from the garden bed and should not be composted.

Q. I am looking for a colorful companion to some early-spring flowering bulbs. A friend suggested the low-growing anemone.

A. Greek windflower (Anemone blanda), is an early-blooming, spreading perennial that works well as a colorful ground cover with spring bulbs. Hardy from zones 5 to 8, it prefers moist, partially shaded (and sheltered) conditions and will spread through runners and seed if planted in the right site. The attractive, fernlike foliage forms low mats, and the white, blue or pink flowers with yellow button centers resemble daisies. Both the spring bulbs and the windflower plants will die back after blooming, creating space in the garden bed for emerging warm-season perennials.

Q. Every spring I become entranced with the different types of poppies, especially those in containers. Which are best for Chicago?

A. Early spring is a fine time to appreciate poppy species, since quite a few are considered cool-season annuals and their seeds can be directly sown into the ground or the tiny transplants can be carefully moved to a container or garden bed (poppies’ taproots resent frequent disturbance). 

• The Iceland poppy (Papaver nudicaule), grown as an annual, has a fragrant flower, 1 to 3 inches across, in salmon, pink, orange, white or red. Its petals resemble crepe paper, and the plant grows to 2 feet. Recommended cultivars are ‘Champagne Bubbles’, ‘Sparkling Bubbles’ and the more compact ‘Wonderland’ series.
• The Shirley poppy (Papaver rhoeas), found naturalized throughout Europe, is considered an annual that can self-sow. Fat, furry buds open to single, double or semidouble nodding flowers in red, white, pink or yellow. These poppies, like the others, prefer full sun, good drainage and an even supply of moisture. They will grow to 2 feet and bloom in spring to early summer.
• The California poppy (Eschscholzia californica) is the famous orange California native that grows 12 to 15 inches. The beautiful ‘Thai Silk’ series includes salmons, pinks, reds and golds. Sow seeds directly into containers or transplant with care.
• The Oriental poppy (Papaver orientale) is the true perennial of the group, when grown in Chicago. It has classic poppy characteristics — dissected basal foliage; large, hairy buds on single stems; wavy, textured petals, often with black splotches at the center; a dislike for winter wetness and a desire to stay in one place. Oriental poppies bloom during early summer.

Q. I am tempted by the gorgeous azaleas available now in florist shops. Is it possible for me to plant them in my garden in spring?

A. Although all azaleas are members of the Rhododendron genus, the florist azaleas are particular hybrids well-suited as indoor plants since they are not hardy enough to withstand Chicago winters. But don't let that deter you! A fully budded indoor azalea plant will provide nonstop blooming color for six to eight weeks this winter. After May 15 (the average last frost date in Chicago), take your azalea plant outside for the summer and place the pot in a partially shaded location in your garden. Before an autumn freeze, bring it back indoors to its original location in a bright, cool spot. At all times, keep your plant well-watered, and remove the faded blooms immediately to prolong the flowering period.

Q. What can I do to prevent powdery mildew from attacking my phlox and zinnias?

A. Powdery mildew is a late-season fungus that favors hot, humid days, cooler nights, and mornings heavy with dew. Interestingly enough, rain does not promote this mildew as it does other fungal disorders. Symptoms include a white-to-gray powdery appearance on leaves, new shoots, stems, buds, and flowers. In some cases, the leaves turn yellow or brown, curl up, and drop off the plant. Flower buds might be distorted or stunted. This fungus also attacks vegetables, fruits, and woody plants as well as other herbaceous plants. The damage is often more aesthetic than life-threatening. Some of the most susceptible plants to this disease include lilac, sycamore, dogwood, crabapple, rose, zinnia, phlox, and beebalm.

When choosing your plants, select varieties that are resistant to powdery mildew. Allow enough space between individual plants, since poor air circulation and overly dense plantings encourage mildew. Water your plants early in the morning, and try to put the water directly into the root zones, not on the foliage. Avoid handling plants when they are wet, since the fungus can be spread on your clothing, gloves, or tools. Make sure plants that require full sun are indeed receiving full sun. If mildew is detected early in the season, approved fungicides can be used to discourage its spread.

Download more information on phlox in Plant Evaluation Notes #13.

Q: My children and I want to plant a butterfly garden. Can you suggest flowers that will attract butterflies?

A: Butterflies frequent sunny, protected sites where nectar flowers abound. They avoid windy, exposed sites. Many native plants are valuable for butterfly gardens. Serious butterfly gardeners consider not only nectar plants to attract butterflies in their graceful adult stage, but also plant host plants for the larvae or caterpillar stage. Butterfly gardeners allow for feeding and damage caused by the caterpillar stage in order to complete the life cycle. Gardeners should refrain from using insecticides that may be harmful to visiting butterflies, bees and other pollinators. Some plants for attracting butterflies include:

You may also want to consider hosting a complete butterfly or moth life cycle with plants such as these:

• Dill or parsley — Both are host plants for purple swallowtail butterflies. Plant enough for you and the caterpillars to feed on.
• Milkweed — It is a host to monarch butterflies.
  Cabbage, broccoli and Brussels sprouts — These are the preferred hosts to white cabbage butterflies. Leave one or more plants untreated with insecticide for the insects.
• Tomatoes — Tomatoes are hosts to hornworm sphinx moths, which are fairly large and attractive in the adult stage. By the time they start to defoliate the tomato plants, you may be tired of homegrown tomatoes. The parasitic wasps present as small larvae attached to the backs of the tomato hornworms are a natural biocontrol that endlessly fascinates children.

Q. What is a rain garden?

A. A rain garden is a natural or constructed depression intended to mitigate stormwater. The plantings in a rain garden allow water to percolate into the soil, reducing runoff into storm sewers, reducing erosion, and protecting ground water quality. In addition to being attractive, a rain garden generally requires less maintenance than a lawn and provides valuable habitat for wildlife.

Considerations when planning a rain garden include available sun, size of desired garden and lot, underground utilities, and plant variety. Keep in mind that smaller gardens have less room for variety. Also, because water only stands temporarily, rain gardens are not breeding grounds for mosquitoes.

It's best to install rain gardens in full sun rather than under large trees. Select native plant species that can tolerate periods of wetness as well as dry periods. Installing plants rather than seeding is also recommended. Plants suitable for rain gardens include red chokeberry (Aronia arbutifolia), red twig dogwood (Cornus sericea), New England aster (Aster novae-angliae), cardinal flower (Lobelia cardinalis), Joe-Pye weed (Eupatorium purpureum), and switchgrass (Panicum virgatum).

Q. I have some beautiful potted chrysanthemums I purchased from the nursery. If I plant them directly into the garden, will they return next spring?

A. Although many garden mums are considered hardy, there are some precautions you can take to encourage their healthy return. Potted mums should be planted directly into the ground in a very sunny location as soon as possible so that they can develop a sturdy root system before winter. Water the plants well to encourage root growth, but do not apply fertilizer until next spring. When the foliage browns later this fall, cut the plant back to several inches, but apply mulch only after several hard freezes. At that time, mulch the plants with 6 to 8 inches of shredded material to help keep the ground temperature relatively constant. Remove the mulch early next spring as new growth appears. Pinch the new shoots regularly until early July to encourage full-bodied plants.

Q. What plants should I use in a rooftop garden?

A. There are a number of things to consider when thinking about planting a rooftop garden. These considerations include cost of installation, maintenance, as well as the type of roof and load-bearing structure. Planting in containers may be a simple, economical alternative to a planting bed. Generally, rooftops are considered to be hostile environments, particularly due to wind and sun exposure. Characteristics of plants appropriate for rooftops include short habit, small leaves, sun and wind tolerance. Plants must also be cold hardy for our region and preferably drought tolerant.

Examples of perennial plants installed on the rooftop garden at the Daniel F. and Ada L. Rice Plant Conservation Science Center at the Chicago Botanic Garden include lesser catmint (Calamintha nepeta); harebell (Campanula rotundifolia); dianthus, specifically Dianthus gratianopolitanus 'Firewitch;' sedums (Sedum spurium 'John Creech') and (Sedum acre 'Aureum'). Each of these would be appropriate for rooftop beds or containers. Please be aware that containers require winter protection.There are many constraints and considerations involved in building a rooftop garden. 

Q. What is the best way to care for clematis?

A. It is important to plant clematis in a location where the top of the plant will receive full sun and the roots will be shaded and cool. Organic matter such as compost and leaf mold can be added to the soil to help retain moisture. A two- to three-inch layer of mulch will also help retain moisture, but take care to keep the mulch away from the stem. Well-drained soil is essential. When planting clematis, it is important to make sure that the crown of the plant, the area where the stem meets the roots, is planted one to two inches below the soil level. Fertilizing clematis is not necessary. Clematis do not like their roots disturbed and do not transplant well.

Q. I have recently installed a soaker hose system throughout my garden. How long do I let the water run in order to water adequately?

A. The amount of time a soaker hose should run depends on the length of the hose, whether it is buried or on the soil surface, what type of plants you are watering and whether or not it rained that week. For herbaceous plants, water must seep down only 6 to 8 inches. Woody trees and shrubs, which have deeper roots, require a longer soak. Most hoses are rated by the number of gallons of water they emit per foot over a one-hour period. As an experiment with the water pressure, turn the hose on for one hour and then actually dig with a spade in different areas and see how far down the water has reached. Keep a record of how deep the water seeped in the different garden areas, and let that be your guide for future waterings. In general, plants require one inch of water per week, spread throughout the root zone.

Q. How do I know if a mature stand of daylilies needs division? When and how do I do this?

A. You can consider dividing your daylilies if they appear too densely crowded, if their flower production is less than normal or if they haven’t been divided in 10 years. By digging the clumps in late August to early September, you give the new divisions a chance to settle their roots before frost arrives. Water the plants well a day or so before you dig and choose a cool, cloudy day if possible.

An established clump will have an extensive, fibrous root system. Using a sharp spade, dig the clump, shake off excess dirt and lay the plant on its side. With the spade or an electric hedge trimmer, make clean cuts through the foliage and roots, either halving or quartering the clump. Trim off any broken roots and foliage and replant each section in your garden. Provide even moisture for these plants right up to frost. Daylilies prefer full sun but will tolerate partially shaded conditions.

Q. Please advise on special winter protection for my garden plants.

A. Many winter injuries common to plants in the Chicago area can be avoided with a few precautionary practices:

• Since evergreens continue to lose moisture through their needles all winter long, they need a healthy supply of water in the root zone to avoid winter burn. During short periods of winter thaw, consider watering all evergreens, especially the shallow-rooted, broadleaved rhododendrons, azaleas and boxwoods. Antitranspirant sprays can be applied to susceptible plants not only before winter begins but also again in periods of thaw.
• When shoveling your driveway or sidewalk, distribute snow loads equitably around small plants.
• Deer browse twigs, buds and many evergreens. Deer repellents are numerous and must be rotated constantly for best success.
• Before you prune out any brown winterkill areas on evergreens, wait until the new growth has come in.
• Try not to walk repeatedly on frozen turf.
• When small woody plants or perennials heave out of the ground during periods of freeze/thaw, gently press them back into the ground with your hands—don’t stomp on the earth around them.
• If you haven’t already done so, mulch garden beds with evergreen boughs, several inches of healthy shredded leaves or compost—only when the ground has frozen hard and if there is no snow cover.
• Wrap the trunks of young trees with protective wrap (and remove it as soon as spring arrives) to lessen the damage caused by temperature fluctuations.
• Monitor trees for animal damage, carefully remove snow from shrubs and protect plants from salt spray.

Q. What insect or disease would cause the flower stalks of my beautiful delphiniums to become twisted and their flower buds to curl and blacken?

A. The cyclamen mite is a damaging pest of indoor greenhouse plants such as African violets and begonias, as well as outdoor annuals and perennials including snapdragons, geraniums, ivy and delphiniums. The microscopic mite lays eggs in moist, dark places, and the developing young larvae feed on plant and flower tissue, creating the damage you have described. Stems can thicken and twist into deformed shapes while the flower buds often contort, blacken and fail to open.

Early detection is the key to preventing the spread of this mite to nearby susceptible plants. Because mites are impossible to detect without a microscope, they can easily spread on contaminated clothing, gloves and other gardening tools. Remove and discard all infected plants from the garden. Do not plant susceptible varieties in the same garden space since adults overwinter in the soil. Approved miticides have limited success. Take care to buy healthy transplants and isolate any houseplants that appear infected.

Q.  What is the difference between aggressive and invasive plants?

A.  The Chicago Botanic Garden defines an invasive plant as “a species, usually nonnative, that is able to establish itself within existing native plant communities and is posing a threat to the integrity of the community.”

An aggressive plant is one that spreads faster than preferred, or into an area of your garden where it is unwanted. A plant may be aggressive in one area of a garden or neighborhood and well behaved in another.

Q. I am fascinated by the use of flowers in preparing certain food dishes. Are there some basic guidelines to follow when choosing the flowers?

A. Edible petals are creative additions to desserts, teas, salads and fruit dishes, as well as charming decorations for most vegetable and meat preparations. Not all flowers are edible, however! Check with a reputable reference before consuming flowers or other plant parts. The American Medical Association publishes a paperback guide entitled The AMA Handbook of Poisonous and Injurious Plants. Avoid using flowers from the florist or flowers that have been sprayed with pesticides or fungicides. Use only flowers you have grown yourself or ones sold as edible in the produce section of stores.

A few popular suggestions to start you on your way include roses, marigolds, lavender, pansies, violets, apple or crab apple blossoms, geraniums (Pelargonium, that is), calendulas, tulips, tuberous begonias, honeysuckle, nasturtiums, lilacs, dianthus and certainly the flowers of all herbs.

Pick the flowers early in the morning, wash the blossoms and dry them thoroughly on paper towels. Decorate hot dishes at the last minute since steam will wilt the flowers quickly. Cold or frozen dishes may be decorated ahead of time.

Q. When is the best time to divide perennials?

A. Perennials can be divided in either spring or fall. As a general rule, divide spring-blooming plants in the fall and fall-blooming plants in the spring to avoid disrupting their bloom cycles. The majority of perennials are divided in spring when temperatures are cool and soil is moist. Dividing perennials in spring also allows plant roots to become established over the course of the entire growing season. When dividing plants in the fall, allow ample time for roots to become established before winter. For questions regarding dividing specific plants, please contact Plant Information Service.

Q. Why doesn't my evening primrose bloom?

A. All evening primroses (Oenothera) require good drainage and at least six hours of full direct sun per day. Evening primroses that are planted too closely together may also fail to bloom properly; therefore, it will be necessary to divide the plants.

Q. Can hellebores be grown in the Chicago area?

A. Hellebores can be a fascinating addition to both sunny and partially shaded gardens throughout the Chicago area. The two familiar to gardeners here are the Lenten rose (Helleborus orientalis) and the Christmas rose (Helleborus niger). Both are clump-forming perennials with evergreen foliage and lovely nodding blossoms in colors ranging from creamy yellow to almost maroon. Perhaps the most unusual feature of these plants is their bloom time: Christmas rose blooms in late winter and Lenten rose in very early spring. The flowers can persist for up to eight weeks if the plants are well-sited. They prefer partially shaded conditions in moist, well-drained soil with lots of organic matter added. Best results come from mulching during hot summers to keep a good supply of moisture available and mulching during the winter to keep drying winds from tearing the foliage. These species and more are on display at the Garden.

A.  The cool, damp, cloudy spring we had this year is conducive to many fungal infections. Some of the more common fungal problems affecting hostas are anthracnose and botrytis. This season, Plant Information has seen many cases of hostas infected with botrytis, which can be prevalent in cool, wet weather. Botrytis on hosta first appears on foliage as water-soaked spots that begin small and increase in size. As the spots enlarge, cinnamon to dark tan rings can sometimes be seen within the lesions. Lesions can also travel down to the petiole of the plant. Anthracnose can affect hosta during warm, wet weather. Symptoms appear as large, irregularly shaped, tan to brown spots with dark borders. The centers of the spots can fall out, giving the plants a tattered appearance. 

Cultural practices can help control both of these fungal diseases. Supplemental water should be applied early in the day so leaves have plenty of time to dry and do not remain wet for an extended period of time, which can facilitate the spread of fungal spores. Water should also be applied to the soil at the base of the plants, and not to the foliage. Plants placed too close together should be thinned to allow for better air circulation. Infected plant leaves should be removed and destroyed to eliminate inoculum. Pruners used to remove leaves should be sanitized with rubbing alcohol or a ten percent bleach to water solution to keep from spreading the fungi to other plants. Fungicidal treatments may be applied to healthy foliage as a preventative. Please contact Plant Information Service at (847) 835-0972 or Click here to show mail address for accurate diagnoses and appropriate fungicide recommendations.

Q: Please advise on the best time to prune hydrangeas.

A: Hydrangeas require differing pruning times; therefore, it is critical to know which type you have before you prune. In addition to using the techniques explained below, always remove any winter-damaged branches in early spring.

• The climbing hydrangea (Hydrangea anomala ssp. petiolaris) grows to 50 to 60 feet and only requires pruning to keep it within its boundaries. Prune in early March.
• The smooth hydrangea (Hydrangea arborescens) flowers on new wood and should be pruned down hard to 1 foot in early March. This species propagates itself by sending up many ground-level suckers, which may also be cut out. Failure to prune regularly results in a top-heavy shrub that flops to the ground by midseason.
• The bigleaf hydrangea (Hydrangea macrophylla) flowers on old wood and should be pruned shortly after it flowers. Gardeners should not wait too late into fall before pruning because late-season pruning can stimulate tender new growth that might be killed during winter.
• The panicle hydrangea (Hydrangea paniculata) and its cultivars also flower on new wood but don't require the drastic pruning of the smooth hydrangea. They will look best if one-third of the old growth is pruned back in late winter. If unpruned, these cultivars can reach 20 feet, which may be too large for certain landscapes.
• The oakleaf hydrangea (Hydrangea quercifolia) flowers on old wood also but is often left unpruned since its spreading habit is quite attractive. The huge, 12-inch flowers are quite ornamental and will lend a late-season interest to the autumn garden. If the terminal buds of this type are killed off during winter, the plant will not flower. 

Q: My peonies have overgrown their space. When can I divide them?

A: Fall is the best time to divide and transplant peonies. Although peonies do not require regular division, when they begin to overtake an area or you find them growing in too much shade, it is time to move them. Plants transplanted in the fall will have plenty of time to establish their roots and still produce spring blooms. Dig up a clump of roots, carefully separating it from the main plant. Leave healthy stems and leaves attached. Using a sharp knife, cut divisions with at least three to five buds, referred to as eyes. The eyes will grow into next year’s shoots. Plant the divisions approximately 1 inch deep. Planting them deeper prevents the plants from blooming next year. Transplants take approximately three years to exhibit full blooms.

Please contact Plant Information Service at (847) 835-0972 or Click here to show mail address for additional information.

Q. Please advise on the correct time and procedure for dividing iris.

A. If you want to divide bearded iris, do so after it flowers, but before August. With a sharp, sterilized knife, cut the rhizome into pieces containing a set of leaves and healthy roots. Plant the pieces 1 inch deep, and cut the foliage down to a 6-inch fan that faces away from the planting circle. Siberian iris (I. sibirica) can be divided in July by digging up the entire clump with a sharp shovel and then separating the clump into as many sections as you want. For an established clump, this might require a pruning saw. Replant the sections in full sun at the same planting depth as the original clump. Early or spring-flowering little irises (I. danfordiae, I. reticulata) can be lifted, separated and replanted in fall, although this is often not necessary since they tend to naturalize by themselves.

Q: Can I transplant perennials in the fall?

A: Although most perennials become available and are transplanted in the spring, they may be planted throughout the growing season—including early fall—as long as they have not gone dormant. Root growth can continue at lower temperatures until the ground freezes.  Some plant species prefer to be transplanted from late summer to early fall (through mid-October). Fall transplanting is especially recommended for peony plants because it gives them time to develop a good root system before the ground freezes while preparing them for a spring bloom. Other species that respond well to fall planting include daylily (Hemerocallis), iris (Iris), tulip (Tulipa), and other spring-flowering bulbs, corms, and tubers. Follow the recommended planting practices for each specific plant species.

Please contact Plant Information Service at (847) 835-0972 or Click here to show mail address for additional information.

Q. What variety of lavender is the best for planting in our area? I'm especially interested in an intensely fragrant variety.

A. Although there are over 28 species of lavender grown today, most are not reliably hardy in the Chicago area due to our cold winters and heavy, wet winter soil. The English lavender, Lavandula angustifolia, and several of its cultivars, however, are worthy additions to both your perennial and herb gardens. And interestingly enough, the English lavender flowers contain a very high concentration of the aromatic oil glands responsible for lavender's fabulous fragrance.

You might try any one of the following cultivars: 'Munstead' (which grows to 16 inches) or 'Munstead Dwarf' (12 inches), 'Jean Davis' (15 inches with pink flowers) or 'Hidcote' (15 inches). Many gardeners report occasional losses over the winter. Try to avoid loss by planting your lavender in extremely well-draining soil in full sun and by mulching it over the winter. In early spring, cut back your plant to a point right above where last year's growth started.

Q:  As temperatures rise and my perennials are emerging, it appears that some of them are very crowded. Should I divide them now?

A:  The correct time to divide perennials depends on the type of plant. Some perennials, such as bugleweed (Ajuga) and tickseed (Coreopsis), may benefit from frequent division every one to three years. Others, such as peony (Paeonia) and plantain lily (Hosta) may require division only every ten years or more. Perennials such as monkshood (Aconitum napellus) and false indigo (Baptisia australis) actually resent being disturbed and can survive well without being divided. 

As a general rule, spring-flowering plants should be divided right after they are finished blooming or in late summer or early fall. If you divide them before they bloom, you may sacrifice blooms for that year. Transplanting earlier in the year allows plants to become established before cold weather sets in. Plants that bloom later should be divided in the spring, just as they begin to emerge. 

Please email Click here to show mail address for more information.

Q. I am interested in cultivating moss on the sides of some of my stone garden urns to give them a natural, aged look. How do I do this?

A. Since moss thrives in a shady, moist environment, containers should not be located in full sun. Mix the following ingredients (proportions are not important):

• moss already growing in your yard, preferably on a stone surface
• buttermilk
• wine vinegar
• corn oil

Apply directly onto the surface of the urns and keep them in a cool, shady spot for about one month. Apply more until moss begins to grow. There are also many paints available that can lend an “antiqued” look.