Composting walnut leavesraises many doubts. This is due to the well-knownnegative effect of walnut on plants growing nearbyDoes it mean that we have to give up the rich source of organic matter, which is the autumn leaves of this tree? We explainwhether walnut leaves can be composted , and advisehow to use walnut leaf compostand when it is better to avoid using it.
Is it possible to compost walnut leaves?
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Allelopathicinfluence of walnut on plants growing nearbywas found already in 1925. Responsible for this is a substance calledjuglone, which is present in the leaves of the walnut(Juglans regia), as well as black walnut (Juglans nigr a), gray walnut (Juglans cinerea) and other representatives the peanut family (Juglandaceae). Juglone has a very strong allelopathic effect on plants and even on some insects. Juglone is considered to be one of the most potent allelopathic substances in the plant world.Juglon content in walnut leaveso varies. The most of it is fall leaves, and the least young spring leaves. The highest concentration of juglon is found in the leaves of older branches at the bottom of the tree.
"Juglone is completely harmless inside walnut leaves , only when it gets into the soil, it turns into a toxic form.Juglone enters the soil by washing it from the leaves by rain, secreting by the roots, and by decaying fallen leaves and green walnut fruit cover.Residual juglone in the soil adversely affects some plant species , causing them to grow poorly or not at all near the walnut. This phenomenon is called nut dieback. "
The plant species particularly sensitive to juglone include:tomatoes, rhododendrons, azaleas, pine, oak, apple tree, grapevine, blackberry, potato, cabbage, crocus, linden, peony, cucumbers, peas and thyme . In sensitive plants, juglone inhibits seed germination and seedling growth, limits the growth of shoots and roots, lowers the number of leaves, adversely affects yielding, and disrupts photosynthetic and respiration processes.
Good to know!
Walnut leaves should be placed in corridors hollowed out by voles. This is a very good way to get rid of voles from the garden.
However, there are many juglone-tolerant plants, they are:onion, Jerusalem artichoke, beetroot, beans, thuja, ash, cherries, red and black currants, lobelia, ferns, tulips, asters, primroses, grasses and elderberry. In addition, juglone has a positive effect on the germination of melon seeds.
The effect of juglon on plants may be different on different types of soil.Heavy, clay and moist soils accumulate more juglone, which remains in them for many years, retaining its toxic form. On the other hand, on dry, well-aired soils, juglone easily oxidizes to form less toxic derivatives. That is why it happens that, for example,peonies growing in the vicinity of a walnut on light soils bloom beautifully and do not get sick
When throwing walnut leaves into the composterwe have to take into account that the juglone will be present in the obtained compost, and after its use it will get into the soil. Then, when growing plants that react badly to the presence of juglon in the substrate, we will not be able to use the obtained fertilizer.But in the case of plant species that are not susceptible to juglone , the use of compost containing walnut leaveswill not pose any risk. However, the juglone introduced into the soil along with the compost will be present in it for a longer time, which will exclude the cultivation of plants sensitive to it.
Therefore, taking into account the properties of juglon,walnut leaves can be composted, but in a separate, well-marked bag or containerThis will avoid the risk of accidentally introducing juglon into the soil. The leaf soil obtained from walnut leaves can be used as mulch or as a valuable loosening additive for substrates for juglon-tolerant plants.
In addition, it is worth noting that the presence of juglon and other phenolic and terpene compounds in walnut leaves causes that their decomposition takes a very long time (even 2 years).Walnut leaves thrown into the composter will slow down the composting process This is also why walnut leaves are better to compost separately.
MSc Eng. Agnieszka Lach
