Healthy soils reduce the risk of disease and pests in plants, including trees. Building or growing healthy soil is thus the best long-term boost to our urban trees, including reducing the effects of PSHB borer infestations.
How can one create healthy soil?
Despite the differences between trees and their individual needs most experts agree that composting and mulching are basic to good tree care.
To do so requires a clear space at the base of each tree. The website www.takingroot.info states that most of “a tree’s roots are in the top 8 inches of soil. Excavation, trenching, and grading can damage roots and kill a mature tree.”
In order to support tree health it thus suggests creating a circle, “1.5 feet of radius for every inch of trunk diameter at 4.5 feet above the ground.”
In the absence of this ideal space it still makes sense to do the best you can to free trees from compaction and to add extra nutrients to make up for the deficit.
Ways in which to compost and mulch
- Leaving leaves where they fall is an efficient way to both compost and mulch your trees. This is especially true in natural forests and where natural forests are mimicked. Such a practice creates an eco-system that supports insect life during winter. When composted, leaves become leaf mould which contains minerals and retains moisture. However, leaves and lawns aren’t great companions which is why you might want to rake your leaves and turn them into leaf mould as an addition to your compost.
- Compost may be made on site or bought from nurseries and used as a water retaining mulch. Compost releases nutrients more quickly than bark or wood chips and so might be a better option to speed up nutrient absorption. However, it is important to keep mulch away from the trunk of the tree to avoid moisture build up. It is also important not to apply too thick a layer of mulch as it can suffocate tree roots, about 5cm in depth seems to be a safe thickness.
- Mushroom compost is great as well. But mushrooms or fungi growing too close to the trunk or elsewhere on the tree is a sign of decay and may need expert attention.
Getting oxygen to the roots and water in dry spells are also important for tree health.
Trees with special needs
Despite all these efforts at supporting trees, not all trees are the same. What one tree considers healthy soil makes another cough, choke, rot or dry out. One tree’s delicious food another’s toxin might be, for it’s the right measure of different elements in specific contexts that for health or ill-health make.
Who its neighbours are also makes a difference, for some plants have symbiotic relationships that for neighbourliness makes and others simply enemies are. Competition for the same resources makes for energy into self-protection directing and the weakest suffer the ill effects of this. So, taking care of your trees is not as simple as one might imagine.
Helping trees adapt to new conditions
In addition, some trees like refugees also are. Transplanted from foreign places they an additional boost of care might in need be. And some, although indigenous, are planted in the wrong place.
Or unloved are; neglected; abused.
Yet a good rule of thumb is that if a tree has made itself at home in a particular spot it’s at home. It may have indigenised. It has taken on local flavours that, like grapes turned into wine, adapts and delivers a new bouquet. Every effort should thus be made to help all our trees adapt to climate change, to electrical magnetic fields unskilfully interfered with, to imbalances in minerals, to toxins in air, water and soil… And to pests.
In short there are so many variables and subsequently no easy answers.
Ideas that I have had include adding natural fertilisers such as rock dust, vermiculture (earthworm compost), green manure teas or fish pond water.
And then there is terra preta which Andrea Rosen from JUFA promotes. The following video explains how to activate biochar so that it adds nutrition to your soil, making it into terra preta. If it works for vegetables, it surely works for trees as well.
Planting comfrey or other green manures at the base of trees is also an option that I like. Different types of groundcovers function as green manures. In permaculture these are particularly popular around fruit trees and so should work for non-fruiting trees as well.
However, given the severity of the PSHB infestation challenge, the best option would be to consult an arborist to provide you with a detailed analysis and treatment protocol for your specfic tree. This is especially important if your tree has been infested with PSHB and you want to boost its chances of survival.
In the absence of an arborist, a horticulturist based at a nursery specializing in trees would also be a good person to consult.
If still in doubt …
Just in case you need to persuade yourself, or others, to invest in the well-being of mature trees, including infested ones, have a look at this infographic put out by the FAO. Trees are vital to healthy urban spaces.
Creating space under your tree:
Why use leaf mold and how to make it:
Building up nutritional count (BRIX):
Tree Care Information:
Best Nursery (in my opinion) in Johannesburg: