Most of us mulch our fruit trees. We mulch for weed suppression, moisture retention, and to protect the tree from mowers and string trimmers. All of these are important, but to your fruit trees, how you mulch is important – it can actually affect how productive your fruit trees are.

Fruit trees depend on a symbiotic relationship with beneficial microbes – specifically a group of mycorrhizal fungi. These fungi form an essential partnership with the roots of the fruit trees. They assist the roots in gathering nutrients and water. In return, the fungi are supplied with food in the form of carbohydrates that the plant produces through photosynthesis. It is a mutually beneficial relationship. Fruit trees that live in soils that are “fungi-dominant” are healthier, use available nutrients more efficiently, are more productive, and have less of a tendency toward alternate bearing.

So what does this have to do with mulch? Your mulch has a significant effect on the microbial makeup of the soil. If the mulch ring is too small, or if you aren’t mulching with the right materials, your soil doesn’t have the building blocks of a healthy fungal colony. Fortunately, this is easy to correct, and the results are almost immediate.

Make that mulch ring bigger
The size of the mulch ring really matters. Fruit tree roots that are covered by turf are living in a “bacteria-dominant” soil. Turf prefers this condition and turf maintenance practices favor it.

In addition, the fertilizer that you put on the lawn is probably not the right kind, the right proportions, or the right frequency for your fruit trees. Turf grasses require nitrogen in amounts that can be detrimental to fruit trees by encouraging them to spend their energy in producing vegetative growth rather than setting fruit buds.

Expanding the mulch ring to at least the drip line of the fruit tree will correct both of these issues. Having a cover of mulch under the entire canopy of the tree will encourage and support a healthy fungal colony. The majority of the feeder roots of the fruit tree are in this area. They will respond to the more fruit tree appropriate nutrition you provide in this zone.

Choose the proper mulch
There are a couple of mulches that will support a fungal soil environment. Fallen tree leaves, shredded native mulch, or a mix of the two are readily available and do the job. Shredded native mulch is material that has been generated from limbs that are usually less than 4” diameter, twigs and leaves. It is recently living material that is high in nutrients that support both soil microbes and the macro-organisms, like earthworms. Fallen tree leaves are rich in minerals. Trees are great mineral extractors and 50% – 80% of the minerals end up in the leaves. As they break down in your mulch ring, these minerals are returned to your soil, and therefore to your fruit trees.

Mulch should not exceed 4” – 6” deep after it has settled. If you are using fallen tree leaves, or a mix of leaves and native mulch, this may mean that you start with a layer that is 8” – 12” deep. It will reduce in volume within a couple of weeks. Keep the mulch pulled back several inches away from the base of the trunk of the tree. The only mulch I use pulled right up to the trunks and stems of plants is pine straw. It “breathes” and does not cause any issues. I often put a “donut” of pine straw right around the trunk and then finish mulching with fallen tree leaves. This suppresses weeds beside the trunk, and keeps a nice, neat appearance.

All mulch should be applied evenly under the entire canopy. No piles or “mulch volcanoes” please!

Inoculate your soil
A fungal colony can be established faster if you inoculate your soil before you mulch. There are several ways you can do this, but here is an easy way with locally available materials:

1.) Remove existing mulch and all turf grass from the trunk all the way to the drip line, at least. A foot or so farther would be better.
2.) Rake loose topsoil away, especially if it is heavy clay or deficient in organic matter. It’s alright if you reveal a few of the roots here. The next step will address this.
3.) Replace the removed top soil with Arbor Gate Organic Soil Complete over the entire new mulch ring. You can top dress as much as 1” – 1 ½” deeper than the original grade. This blend has all of the components that will stimulate the establishment and growth of a mycorrhizal fungal colony. You do not have to work this into the soil. Nature will do the work for you over the next few months.
4.) Broadcast Arbor Gate Organic Blend at the rate suitable for the type of fruit, time of year, and age or size of the tree. In addition to its nutrients, this slow release organic fertilizer contains eleven species of mycorrhizal fungi and the microbial food to support them.
5.) Place your mulch material evenly over the new mulch ring. The initial depth will depend on the materials you have chosen, but should be the same depth all across the ring. If you are using just native mulch, you can apply 4” – 6” which will settle a bit in a few weeks. If you are using just fallen tree leaves, you can apply as much as 10” – 12”. This will soon settle to about 4” – 6”. If you are using a mix of the two, you will have to play it by ear depending on the ratios of each. Your resulting mulch depth after settling should be 4” – 6” under fruit trees; deeper than in your perennial beds.
6.) Foliar feed your tree with a sea-based, mineral rich liquid product. This will provide minerals that will translocate from the leaves to the roots, sending signals to the microbes and kick starting the partnership. It’s good for the trees anyway. I like to use a hose end sprayer to make quick work of it. While you are at it, spray the new mulch bed down with the solution, too.

This technique is a “top down” soil improvement method that really works. It will make a difference in the overall performance of your fruit trees for years to come. You will need to maintain a constant mulch ring around the trees and continue regular applications of Arbor Gate Organic Blend as your slow release organic source of nutrition. The fungi (and their friends) will do the rest!