The city gardener

Wondering what to plant in those tough spots?


As a Master Gardener, people ask me lots of questions about their yards, but probably the most common type of question is “I have a spot that’s hard to grow things in. What should I plant there?” So, this is the first of a short series of articles on plants for difficult areas that many of us in south Minneapolis have to deal with. This month, we’ll cover some tips for growing plants on boulevards and under black walnut trees.
A boulevard is the narrow patch of land between the sidewalk and the street. Because boulevards are right next to the road, they often contain high levels of road salt, which is damaging to many plants. They are often dry, with poor quality compacted soil. They may be used as a frequent pathway when people park on the street. However, there are a number of perennials that tolerate these conditions well and can be used to beautify your boulevard.
Before we get into it, I want to note that it is important to follow city ordinances on boulevard plantings, and remember that this area may be dug up or damaged if it is necessary for road construction, utility work, or other purposes. In general, it is permissible to plant flowers and grasses on the boulevard, but make sure that they do not obstruct the sidewalk or street, or make it difficult for drivers to see around a corner. If you want to plant a tree on the boulevard, you will need to get a permit from the Park and Recreation Board. Also, before you dig, it is recommended to contact Gopher State One Call and have utility lines marked. Better safe than sorry!
Plants that will tolerate a sunny, dry boulevard include yarrow, bearded iris, purple coneflower, aster, phlox, sedum, sea holly, and speedwell. If your boulevard is shady, try astilbe, foxglove, vinca, or verbena. Daylilies and hostas are also common on boulevards and they tolerate a wide range of conditions.
If you do want to grow grass in your boulevard, try fine fescues, which are much more tolerant to road salt than the common Kentucky bluegrass. Another good option is a short native grass such as blue grama, which is a particularly rugged species that grows well in dry sites and full sun.
Before you start planting, prep the boulevard by removing grass and weeds and breaking up compacted soil. If you have a tree on your boulevard, be careful not to damage the roots. Adding organic matter such as compost can also help improve drainage and provide nutrients. Also, make sure the soil stays just below the level of the curb so soil and mulch don’t run off into the street. The middle of the boulevard should ideally be two or three inches lower than the curb. You may need to remove some soil to achieve this.
Although boulevard gardening can be challenging, planning ahead and choosing plants well-suited to the conditions makes it much easier!
Next, we’ll talk about planting under black walnut trees. Black walnut trees are common in south Minneapolis and as you may know, not all plants grow well near them. The bark, roots, leaves, and nuts of black walnut trees contain a toxic compound called juglone, which help the tree outcompete other nearby plants. Plants sensitive to juglone may die quickly when planted near a black walnut tree. Signs of juglone toxicity include wilting, yellowing leaves, and stunted or slow growth.
Unfortunately, there is no way to reverse juglone toxicity or remove the compound from the soil. Instead, for any plantings within 50-60 feet of a black walnut tree, choose juglone-resistant plants. You can also try planting non-resistant species in raised beds or pots, but be sure to remove any black walnut leaves, nuts, or stems that fall onto the soil.
Luckily, there are many juglone-resistant plants that grow well in our climate. Suitable perennials include hollyhock, Jack-in-the-pulpit, astilbe, coral bells, bee balm, phlox, and spiderwort. For trees and shrubs, try serviceberry, river birch, mock orange, sumac, and viburnum, among others. If you are planning a vegetable garden near a black walnut tree, onions, beets, squash, carrots, parsnips, beans, and corn tolerate juglone best.
For more information on these and other tough sites, check out the publication “The Best Plants For 30 Tough Sites” from the University of Minnesota Extension. You can access it for free through the University of Minnesota Digital Conservancy, at
For more information, check out the University of Minnesota Extension Yard and Garden website. Extension resources are written by experts and contain the latest and most reliable research-based information. Happy gardening!


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