We invested a lot of time and money in our garden a couple of years ago but are concerned about how some of the plants are growing. Our river birch especially concerns us. What steps can we take to help our garden?
— Nick Valenti, Lombard
Plants that do not perform well in the garden can be very frustrating. I have had my share of plants that have failed at home, and I’ve found that the two main causes were not watering enough to get them established and trying to grow plants that were not well-adapted to my garden. Different gardeners and experts can also give conflicting advice. This makes finding a solution or a course of action even harder. I will provide some general considerations for you to review and consider.
A good place to start is to make sure that you have selected the right plants to meet your design objectives and for your garden’s growing conditions. Choose plants with cultural needs that match the conditions in your garden rather than plants that just tolerate your planting zone. I see many home gardeners with plants that are not sited well for what the plant needs and how the plant grows. It may seem obvious, but as an example, sun-loving plants need to be in the sun while shade-loving plants need to be in shade. Autumn Joy sedum prefers sunny, dry conditions, while astilbe prefers shade and moist, well-drained soil. Panicle hydrangeas are generally easy to grow and flower most profusely in full sun but will tolerate some shade. Too much shade will result in reduced flowering and spindly plants. There are many different cultivars of panicle hydrangeas available, so choose one with a mature size that matches your space.
Selecting the wrong plants for your garden’s growing conditions usually results in poor plant performance and extra maintenance. Your garden’s soil conditions will affect the growth of your plants, too. There are a variety of soil types in the Chicago area, ranging from sandy to heavy clay. A river birch can develop chlorotic, or yellowed, leaves when grown in heavy clay soils that have a high pH. River birch prefers moist conditions but can adapt to drier sites. Other trees are more tolerant of these conditions. Some maintenance practices can help. Amending the soil around the tree with elemental sulfur can reduce the soil pH. Long term, however, it may be best to choose a different tree. Avoid using yews and arborvitae, which are deer favorites, if there are a lot of deer in your area, or plan on netting them every fall. Boxwoods are not browsed by deer.
Soil moisture conditions (such as dry, moist but well-drained, wet and poorly drained) are important to consider when siting plants. Choosing plants that are suitable for these conditions will greatly improve your success. Spreading yews do not do well in wet soil conditions. Yew foliage that begins to yellow is probably getting too much moisture. The common red twig dogwood (Cornus sericea) is tolerant of wet conditions and easy to grow, while the flowering dogwood (Cornus florida) is very difficult to grow in Chicago.
Good site preparation and proper planting techniques, along with proper maintenance, will improve success too. Garden sites around new construction often have heavily compacted soils that need to be loosened up and amended with compost prior to planting. Sites with new homes may have very little topsoil left. Trees are often planted too deep — you should be able to see the root flare just above the ground. I like to plant 2 to 3 inches high in heavy clay soils. The base of the tree’s trunk will widen out at the root flare. The root flare can be inches below the top of the burlap of a balled and burlapped tree. The stress of planting a tree or shrub too deeply may not become visible until the plant has been growing for a few years.
Knowing the plants you currently have and the growing conditions in your garden will help a gardening expert provide you with good advice. The Chicago Botanic Garden’s Regenstein School offers a wide variety of gardening classes.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at [email protected]. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.