Portland Oregon Landscape and Tree Care presentation on lasagna gardening

Soil ~ Root Feeding ~ Fertilizing

Text and Images Copyright 2002-2008 by Mario Vaden

Proper feeding involves beneficial mycorrhizal fungi ...

We provide service to aerate soil and aid the nutrient process for plants, by adding organic matter and beneficial mycorrhizal fungi near roots. This will be explained here for two reasons. First, you may choose our service to do this for you. Second, you may want to take care of this kind of tree care yourself. If you find this information useful, be sure to visit the Soil Care page.

Deep root feeding
Small microbes like beneficial fungi and bacteria can occupy pore spaces between soil particles and make the area less susceptible to compaction. Too much fertilizing can kill beneficial microorganisms and make soil more susceptible to soil compaction.

If you are unfamiliar with mycorrhizal fungi; those are microscopic fungi that benefit trees. In fact, the Chanterelle mushroom that is available in grocery markets and gourmet restaurants is the above ground fruiting body of one of these mycorrhizal fungi.

Many mushrooms are from mycorrhizal fungi. And many of us are much more familiar with mycorrhizae than we might realize.

Adding mycorrihizal fungi to soil around trees can be very beneficial. Fertilizer may be applied during this operation, but can be best applied separately if needed at all.

Fertilizing, especially a single larger dose, can cause damage to life in the soil. In addition, trees have been damaged by growing too large or too quickly due to fertilizer programs. Abundant fertilizer will usually produce leaves that become large – larger than may occur in a healthy natural environment. That yields more leaf surface area for wind to grab.

Big leaves provide more surface area for rain-water to weigh-down. When branches elongate too much, that’s extra leverage provided in favor of damaging weather, enabling weight of ice or snow to crack or snap the wood.

There is a big difference between feeding and fertilizing for successful tree preservation. Feeding is primarily accomplished by the tree – what it does. A tree “feeds” on what is available in the soil. Fertilizing is what man does, what man provides. Or what animals and nature may contribute and provide; deposit.

The significant part of our tree nutrition care deals with soil and needs of trees. Most often, deep-root-feeding is not a need because most tree roots draw nutrients from near the top 12 inches of soil. Those are shallow roots. So shallow-root-feeding is an appropriate need.

There are at least 3 ways to add material (not just fertilizer, but “material”) to the soil around trees. One way is with machinery that pressurizes air and BLASTS the soil surface. This opens cavities which can be filled with improved soil. One benefit of this method is minimal damage to roots. Drawbacks include:

1. The equipment is loud and causes disturbance in residential areas. 2. The soil that’s blasted from the ground is a source of wind-borne erosion. 3. Plants, automobiles, windows and other items become coated with filth.

Another method requires equipment to inject high-pressure water / liquid into soil. That shoots fertilizer or amendments into the ground at high-velocity. Benefits include speed and ability to send amendments – in solution - into soil. It’s a fast in-and-out procedure. The down-side is that:

1. The holes are only large enough for microscopic additives and liquid, but too small to add generous volumes of blended soil with organic matter and compost.

2. That injection method can exceed merely breaking soil compaction. It can also demolish soil structure in the injection zone and start mushy spots. Mushy soil with rain and wind are a bad combination for trees in winter.

An auger method has several benefits, which are: 1. Tools that are quiet. 2. The equipment is small. 3. The mini-auger breaks-up compacted soil. 4. Soil is not scattered into the air; thoughout the neighborhood. 5. Excavated holes are large enough to add organic matter and mycorrhizal fungi to the earth.

Sometimes, pressurized injecting soil is more practical if root systems are so thick and numerous that an auger can't drill into the ground. In that case, injection may be the method to choose. Maybe no method of opening the soil would be the right course of action. Each tree should be evaluated individually.

Feeding is an important aspect to understand. Trees, in a way, feed themselves. Fertilizer is not food, even though a bag may be labeled as “plant food”. Nitrogen or phosphorus in the soil are not food. Those are more like nutrients. Trees draw nutrients and water from the soil with roots. All of that is sent up to leaves where photosynthesis occurs. After all that happens, there then there is food. Food that the tree produced.

Over 75% of a tree’s energy is sent back to the roots. About 40% of a tree’s energy is exuded by its roots as sugars, proteins, etc. Those exudates produce a nutrition source for good fungi that in return, help to benefit the tree. Good fungi include MYCORRHIZAL fungi. In fact, mycorrhizal fungi can be far more important to a tree than fertilizers.

mycorrhizal tree feeding

What are mycorrhizal fungi? Those are microorganisms that promote and establish MYCORRHIZAE. What is mycorrhizae? A simplified explanation - its the presence of a relationship that has beneficial fungi at the root system, attached to the roots or slightly embedded into the roots. In a way, it’s as if the fungi are an extension of the root system (just not an actual part of the roots). It can be referred to as FUNGUS-ROOTS. The mycorrhizal fungi are part of the tree and root relationship; interaction. The tree roots are also part of the sytem or relationship by aiding the mycorrhizal fungi. And healthy growing plants will have a combination of roots with, and without mycorrhizae.

That mycorrhizae system can be destroyed by compaction, excavation, and pesticides. One hour of heavy equipment traffic at a construction site can destroy a hundred years worth of natural soil development.

Another significant destroyer of mycorrhizal fungi are FERTILIZERS. That’s not a type error. Fertilizers can destroy microorganisms in soil. How does that happen? Fertilizers, EVEN ORGANIC fertilizers, produce salts. Salts can dehydrate and kill good microorganisms. This is crucial knowledge for feeding trees.

The best way to feed many of our trees is by eradicating the presence of soil compaction and promoting mycorrhizae. This is done by adding mycorrhizal fungi and soil amendments that support the heath of trees and microorganisms. Mycorrihizal fungi and trees exchange materials. Tree roots gain minerals, nutrients, water and more. The fungi gain sugars and other compounds. This way, the trees contribute and gain, and fungi contribute and gain - both are giving to, and receiving from each other.

Good soil should contain in excess of 6,000 to 10,000 different microorganisms PER TEASPOON. 1,000 to 5,000 is not substantial. That’s why we maintain a compost and soil stockpile for tree feeding. This special reserve is in a fenced area isolated from pesticide use. This blended soil includes soil, compost and mycorrhizal fungi. In addition, it has been “seeded” (amended) by a batch of forest soil and compost mix. This is to increase the number of beneficial microorganisms.

Mounds of compost can be expected to contain more than 10,000 to 15,000 species of microorganisms. Most of those are beneficial for soil. Commercial products (also called innoculants) contain species of microorganisms. But far less than a mound of good compost. The innoculants are still good.

In our tree preservation and soil improvement program, we take organic compost and combine it with blended soil and mycorrhizal products. This blend is used to fill openings in the soil after we aerate the ground. It’s similar to aerating a green at a country club, but tailored to a tree. This provides not one, but two sources of mycorrhizal fungi.

It is important for people to prevent and eliminate soil compaction. When soil is compacted, bacteria may produce alcohol, and alcohol can kill roots. There are many sources that you can go to for more education about mycorrhizal fungi. If you search on the internet, your first query will probably list enough reading material for hours. Libraries and book stores will also have reading material if you are interested.

Soil tests are available, and fertilizer can be added if analysis verifies a reason. Fertilizer can be applied on the soil surface to preserve natural activity in the aeration holes. There are fertilizers available as mild as bulb food. Instead of relying exclusively on speedy pressurized injections, we prefer to individually core-aerate and backfill the ground with soil / compost blends. If you are going to make an investment in your trees, why spend your valuable funds on speedy in-and-out operations?

Also, if you do discover or determine that you need to add a bit of fetilizer, there is no need to apply it all at once. You can apply it in small doses. Instead of applying, say, 6 pounds all at once, try applying 2 pounds three times at two to three month intervals. That will reduce the concentration of any salts moving down through the soil.

One thing to consider too, if shrub and lawn fertilizers are used in moderation to improvise if you decide to fertilize: some lawn fertilizer products contain herbicides for killing weeds. Those same herbicides that will kill dicots like dandylions, can also kill trees. Never put fertilizer in the soil for trees that contains damaging herbicides.

On the other hand, if we take care of soil properly and use fertilizer sparingly, we shouldn't find ourselves reading labels on fertilizer bags.

The information on this page may be applicable in the same identical fashion if you are growing trees for specialized harvest purposes such as Christmas trees or certain kinds of lumber. Supposedly, in those cases, you will be a sort of expert on that kind of agriculture. Still, much of this information is still applicable - either in part or all of it.