Hello Master Gardeners – I know your website has lots of information about the despised Tree of Heaven but I haven’t seen my particular issue addressed. There’s a huge Ailanthus (at least 50 ft tall) in a corner of my driveway, close enough to the street to qualify as a city tree. I’m pretty sure the city will not allow it to be taken down. On the tree’s shady side (full shade) is a bare and depressing patch of dirt which I’d like to populate with something green and living. Would you have any plant recommendations – and I mean anything e.g. ground covers, vines, shrubs or small trees – for this truly hellish patch of dirt? Thanks for thinking this over and any help you can provide.
Hello! Your query raises a number of interesting points. Tree of Heaven (Ailanthus altissima) has been designated an invasive plant in Toronto and The Invasive Species Centre provides a thorough review of its detrimental characteristics.
One of these characteristics is that Tree of Heaven is allelopathic, meaning it releases toxins, including ailanthone, into the surrounding soil which prevents other plants from establishing nearby. Tree of Heaven is not the only tree with allelopathic qualities. For example, Black Walnut releases a toxin called juglone into the soil. Aspects of the article Landscaping and Gardening Around Walnuts from Penn State Extension are equally applicable to Tree of Heaven. This includes removing plant debris quickly from underneath the tree before it decomposes and using raised beds or planters with liners and new soil, not soil from under the tree (rather than planting directly into the soil under the tree). Once you have established these raised beds or planters, you can proceed with growing your choice of favourite shade plants, both perennials and annuals.
Sadly, many gardeners turn to two other invasive plants for the most difficult areas of their gardens, for example under trees, and these are Japanese Spurge (Pachysandra terminalis) and Periwinkle (Vinca minor). I strongly recommend you avoid these two plants and instead consider using native plants in this shady area. Toronto Master Gardeners has created Garden Guides specifically on this topic, Native Plants for Shade and Native Perennials for Shade.
I wish you all the best with this project. (I, too, deal with a Tree of Heaven on my neighbour’s property!)