Since we began our journey towards transforming the Lyttleton mini-orchard into a productive food forest, we noticed that many of the ground covers and shrubs we planted failed to thrive. Amongst the large number of fruit and nut trees in this small-scale orchard, we have two very large walnut trees.
We had heard that some walnut tree varieties were allelopathic, but had assumed these weren't them, as they were surrounded by other thriving productive trees. Allelopathy is a biological process by which a plant inhibits the growth of another. After further observation, we discovered that they were indeed black walnuts (Juglans nigra), which are allelopathic.
Various parts of plants can have these allelopathic properties, from the foliage and flowers to the roots, bark, soil, and mulch. Most all allelopathic plants store their protective chemicals within their leaves, especially during autumn. As leaves drop to the ground and decompose, these toxins can affect nearby plants. Some plants also release toxins through their roots, which are then absorbed by other plants and trees. Our hearts sank a little when we found out about this.
In the case of our walnut trees, the substance they secrete through leaves, and roots, is called juglone.
Luckily, there is a variety of juglone-tolerant shrubs and plants, many of which have medicinal properties. Some of these are echinacea, yarrow, calendula, evening primrose, witch hazel, elderberry, and common daylily.
Wheew! We will now be planting medicinal ground covers and shrubs, and teaming up with very our own naturopath, Sarah Mann. She will be making homegrown medicinal tea blends and providing advice on medicinal plants, foods and nutrition. How wonderful it is when an obstacle becomes a great opportunity!