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QGRASS ROOTS

I have been watching some British garden shows which are great. They said that if you don’t remove turf from around new trees (at least for the first three years) you can slow their growth by a third. Does this apply to wildflowers planted under fruit trees as well? ALIX LATTEY, TAUPO

AFour members of the NZ Tree Crops Association (treecrops.org.nz) put their heads together to answer your question.

Derek Craig, the National Research Coordinator, said that he too would remove grass cover around newly planted trees and mulch to suppress grass regrowth. The mulch would also shelter the tree roots from summer heat and help retain moisture. Over time, the decomposing mulch would also feed the tree. The reason for removing the grass is to eliminate root competition. Fruit tree roots are very shallow growing, and the grass roots are voluminous and very good at stripping water at the same soil level as the fruit tree roots.

The addition of a flower herbal ley has some of the same problems as grass cover though stress from root competition for water and nutrients would be alleviated by irrigation through summer. However, a more holistic view would counterbalance the water competition with systemwide benefits such as offering insect shelter, nectar, pollen and alternative food hosts plus acting as living mulch to shelter soil and roots.

Fellow Tree Cropper Eric Cairns added that grasses (monocotyledons) exude allelopathic substances into the soil that inhibit the growth of trees. Most fruit trees (except citrus) aren’t all that shallow rooted, but will send their feeder roots to where the nutrients are, so they will be at the surface if a mulch is used. He says wildflowers will compete for moisture and nutrients, but would not be as inhibiting as grasses.

Tree Cropper editor Britt Coker referred to the food forest regime of layering plants to maximise space and out-compete weeds. The benefits of drawing in pollinators outweighs the competition, she suggests.

And finally, our Waikato columnist Sheryn Clothier: “Competing roots can be detrimental in the first season or two of a tree getting established, so clearing or mulching the area within 30cm of the trunk has benefits. But after, an understorey of wildflowers is beneficial to the soil’s ecosystem and therefore, beneficial to the roots.”