YOUR GARDEN — Plant Information

Frequently Asked Questions – "R"

Q. What is a rain garden?

A. A rain garden is a natural or constructed depression intended to mitigate storm water. 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. Where is the best location to plant a redbud?

A. Eastern redbud (Cercis canadensis), is a lovely early spring blooming tree that is relatively small in habit and appropriate for small yards. They should be planted in moist, well-drained soil in full sun or partial shade. Redbuds are very pH adaptable and will grow equally well in alkaline or acidic soil. It's best to plant redbuds in an area with good air circulation to reduce the chance of fungal diseases. Redbuds do not respond well to stress, so care should be taken to water regularly, and keep the tree as disease- and insect-free as possible.

Q. What is the best way to plant a rhododendron?

A. When planting rhododendrons, it is important to select a variety that is winter hardy for your plant hardiness zone, based on the USDA plant hardiness zone map. The Chicago region is zoned 5a and 5b. Rhododendrons should be planted in well-drained, acidic soil amended with large amounts of organic matter. A soil pH of 6 or greater, which is very common for the Chicago area, will need to be acidified by adding sulfur annually. No sulfur should be added to the soil until the pH is determined using a pH test kit or receiving a lab soil analysis.

Water the plant thoroughly before planting. Rhododendrons need to be planted high in a hole approximately one half the depth of the rootball because they are shallow-rooted plants and very susceptible to root rot. The top portion of the rootball should be covered with an acidic mulch such as pine bark to help lower the pH of the soil. The plants should be watered well after planting and mulch replenished yearly, if necessary.

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. Do all rose bushes produce rose hips in the fall?

A. Some rose bushes produce hips (which are actually the fruit or ovary of the plant) after September 1, when all deadheading of roses should stop. Species roses and Rosa rugosa are known for their showy hip production, which extends well into winter and often provides food for birds and animals. Allowing the roses to "go to seed" and produce their hips is an important part of their preparation for dormancy.

Q. How and when do I winterize my roses?

A. Planning for winter actually starts in early fall. Stop fertilizing your roses in early August and stop deadheading by Labor Day to allow the plant to shut down and set hips (seeds) for winter interest. Remove fallen leaves from the garden. It's best not to cut or prune your roses at this time of year as the cuts will not have sufficient time to callus over before winter. Roses should be dormant before winter protection is applied. After several days of below freezing temperatures, create a mound of soil, compost, shredded leaves or evergreens 8 to 10 inches deep over the base of the plant. Mounding keeps the rose uniformly cold, which reduces the chance of damage caused by cycles of freeze and thaw.

Canes of taller or climbing roses can be loosely tied together using twine or fabric strips to prevent damage from winter winds. The canes of climbing roses can also be laid on the ground and covered with approximately 6 inches of garden soil to protect them for the winter. Winter protection should be gradually removed beginning in late March or early April when new growth begins. Take care not to injure new growth. Hybrid tea and English roses, like the David Austin roses, should be cut to knee height after several days with temperatures in the teens. Mound 12 inches of composted manure or lightweight garden soil around the base of each bush. Additional shredded leaves can be piled on over the canes and held in place by chicken-wire cages. If we have not had the required low temperatures by Thanksgiving, proceed with the winterizing anyway. Shrub roses can be pruned for shape but generally do not require any additional protection. Climbing roses are mounded as above, untied from their supports, retied in one place and wrapped with burlap.