Imagine a world in which at least the drip zone of Tree Root Zones were managed for health/longevity and vigor.
This blog post will cover a few things you can do to maximize tree growth, survival rate, health, production (fruit/nut), and longevity. The following instructions should lead to the following benefits to your tree.
1. Reversing soil compaction around the tree, increasing percolation of water, porosity, bettering soil structure and water + air holding capacity which benefits ability to photosensitize and grow.
2. Minimizing root competition from lawn which boosts growth, health, and longevity especially during the immature years of the tree.
3. Localizing an abundant reservoir of bio-available (plant absorbable) minerals and nutrients, while creating a biological hot zone around the tree providing natural benefits to the soil. This includes the restoration of a very biologically active O layer.
This is our current, most common state of root zone management, lawn up to the trunk...or perhaps a small mulch ring. Small in comparison to the canopy of the tree.
Negative effects of managing tree root zones with lawn or small mulch rings + lawn.
Mowers + the weight of human traffic (we're big animals!) maintains a level of compaction one does not encounter on a forest floor. That is why you can "sink" an inch or two into the topsoil of a forest floor, but in a lawn, it is more sturdy, solid, compacted. Compaction means less pore space, less pore space means the soil has a lessened ability to hold air and water, both essential to plant photosynthesis. Compacted soil can be one of the most limiting growth factors that a plant faces. Newly constructed developments, especially within the past decade or so, are notoriously compacted, but we can reverse that. Compacted soil not only has poorer pore space, but directly related to that issue, water has a more difficult time percolating, so more water runs off the surface instead of seeping into the soil.
Lawn gets an early start in up taking available nitrogen and other nutrients from the soil. Because most lawns in the midwest are composed of cool season grasses, they begin growth in late march/early April in many springs, just when many of our native trees are sending sap back above ground, but well before our native trees begin to leaf out. Turfgrass then continues rampant growth throughout May and June trying to reach flowering height so it can set seed by July, we interrupt that cycle through mowing causing the turf to perpetually attempt to reach flowering height absorbing significant amounts of nutrients as long as the soil is moist enough to promote new growth. One positive thing though is, since we mow lawn, it has very short root systems, and tree roots can often monopolize moisture in the subsoil.
When we're trying to establish saplings or even large balled and burlap trees, the trees have to send roots that fight through the tight sod of lawn, inching year by year to find underground niches of available water/nutrients that either the lawn isn't using or the tree outcompetes the lawn for. This competition that lawn provides to establishing trees, is one of the main retardants of tree growth while immature. Most trees if planted correctly and sited well, eventually over come the lawn and establish their dominance, but the lawn still played a retarding role in each of those tree's establishing growth, and possibly the tree's longevity.
Lack of O layer; the O layer (Organic matter layer) within the soil profile is different from ecosystem to ecosystem. A prairie O layer is very thick and well developed unless it's a glade like prairie. O Layers of temperate forest soils are often rich of partly decomposed leaves, twigs, branches, and logs, all the while relatively shallow compared to a Prairie O layer. The O layer in a wetland or boreal forest is often very deep, as organic matter has a hard time breaking down due to too much moisture (anerobic conditions) or not enough heat and unfrozen moisture (boreal forest). The O layer of a lawn (thatch) is typically plain pitiful in comparison to the O layer of a real ecosystem. So our trees are growing without the most biologically active, and nutrient rich layer of the soil profile. We'll talk about reviving the O layer later in the blog.
The Short Version (Recap)
The Many Effects of Compaction
Mowers + human foot traffic maintain an unnatural level of compaction, reducing pore space in the soil which reduces available soil moisture, air holding capacity, and reducing percolation all of which are retardant factors affecting of growth, health, and longevity.
Nutrient and Resource Competition
Cool season turfgrass gets an early jump on available nutrients, and spends a lot of energy spring and early summer trying to flower causing the grass to continue to compete for available nutrients. Turfgrass roots/sod must be conquered by every tree we're trying to establish in a lawn, traditionally, (we're going to discuss a new way) therefor in the establishment years of a tree, they're forced to fight inch by inch through the already established, perennial turfgrass to create their own root zone retarding growth and vigor. Imagine putting a Zinnia in a lawn, and a Zinnia in a container, which will row faster, mature larger, and possibly even live longer?
Absent O Layer
Outside of Deserts, nearly all ecosystems have significant O layers (Organic Matter Layer) which often hold the largest reservoir of bio-avaialble nutrients and biologically activity (soil life). The O layer of lawn is a very thin layer of thatch that cannot start to compare with the value of a forest, prairie, or wetland O layer. Our trees are essentially missing a very important layer of their original soil profile. Lack of O layer also creates highs and lows in soil temperatures and lessened ability to hold moisture in the A layer (topsoil), which is not good for anyone
So we need to flip all of these limiting factors, into reasons why our trees are thriving, live long, and grow vigorously. This requires biomimicry with some modification to speed up, maximize , and sustain nutrient availability + humus production.
Instead of planting our new native tree in a lawn subjected to mowing, foot traffic and lacking an O Layer, we're going to give our newly planted tree a patch of Savanna-like soil conditions and add some deer protection, which is often lacking but completely essential in Midwestern metropolitan property open to deer browse and rubbing.
Have you ever "potted up" a young tree? This means to move it from a 1 gallon to a 5 gallon pot, or a 5 gallon to a 15 gallon pot. When this happens the tree has a chance to expand it's roots, which corresponds with an increased ability to grow above ground in stem/leaf form. When you plant a tree sapling, or 1 gallon or 5 gallon or whatever sized tree into a lawn, you're essentially potting it up, except the pot has no bottom.....or edges.....but this new pot (the lawn) has water and nutrient thirsty turfgrass.....and heavy animals called humans compacting the soil.....and the sometimes heavy machinery, mowing the thirsty grass.
So what can we do to give our new planting a easier time expanding it's root system?
Get rid of the grass. How? Smothering with cardboard if organic, herbicide by the label, if not. Organic method is better for soil biology in the short-term, at least. Tilling and Solarization with black or clear plastic damages soil biology in the short-term, at least.
We've stopped mowing, and stopped walking around the tree. We've also gotten rid of the grass within the recommended diameter circle pictured above.
Ok easy enough, so what's next?
Next we work on restoring the O layer.
We're concerned with restoring a biologically active, moisture retentive, nutrient dense O layer which doesn't significantly form within a lawn, but was part of all of our major ecosystems soil profiles excluding deserts. If you used cardboard to kill of the grass in the rootzone, remove it before adding the below recommended materials.
If you're installing the zone in the fall, get as diverse amount of tree leaves as possible. Some tree leaves aren't very carbon dense and break down quickly like Hackberry, Silver Maple, Black Cherry, Black Locust, Black Walnut, and Honeylocust. Sugar Maple, Black Maple, Oaks, Hickories, Beech Trees, and a few other trees produce leaves heavier in carbon, and longer lasting. Try to collect more of the latter than the carbon-lite leaves.
If you use a strong push behind or walk behind mower that can bag the shredded leaves or mulch them in place, go for a a <1" application of shredded leaves. This is a bit more than would naturally fall in one area, but since they're shredded, they shouldn't last more than 1 year which means the soil biology is releasing their nutrients through decomposition into the root zone of your new tree.
If you can't shred your leaves go for a 2-3" application of un-shredded leaves, but be sure to not pile the leaves directly around the trunk, as that can promote negative fungal activity on the bark of your tree and rot it to death. By the end of the winter the 2-3" application should look like a 1-2" matted application of tree leaves. Shredding the leaves is best for quicker release of nutrients aka decomposition. Though unshredded leaves may be better for attracting beneficial insects due to the micro-habitat created within layered leaves.
If you're installing the zone in the spring, utilize straw bales going for a 3" layer somewhat loosely laid, perhaps 2" if straw is compacted well. Straw won't have the mineral quality of tree leaves, but will provide some trace minerals, nitrogen, and carbon for humus (o layer) formation. Alternatively apply 1-2 inches of leaf compost, or 3-4 inches of regular compost throughout the root zone with 2" of straw on top.
Pictures above Fill the Root zone with fall leaves from as many different species as possible. Then mow all of the leaves up in place or bag them with a mower and spread the shredded leaf matter throughout the zone. Your finished product should have turned the leaves into not much visually, rest assured, there is an abundance of nutrients ready to be released from those leaves.
Maximizing Available Nitrogen + Other Nutrients within the No Mow Zone
The tree leaves or straw will be providing a broad spectrum of minerals as they decompose over the course of 8-12 months after applying. Again, shredding is best, though it is more difficult to shred straw without an actual leaf shredder. These materials are high in carbon and many minerals, promoting the formation of the O Layer (partly decomposed organic matter). These materials are not very dense in nitrogen though, and to make sure your tree has an abundance of this key nutrient available, the rootzone will need some nitrogen rich materials added throughout the growing season (Late March-September)
After the first growing season
The rootzone of your tree should be developing humus (mostly decomposed organic matter). It should also be inhabited by beetles, ants, spiders, and many other insects moving throughout the O layer. You can add a log or two into the root zone which may attract beneficial insects. As long as it's not buried, it wont' significantly affect your Carbon : Nitrogen ratio balance, though it should be colonized by the fungal community over time which may be connected with your establishing tree exchanging nutrients and biochemicals. If you're limiting your walking in the zone, you should also feel the soil softening/aerating after the first growing season, perhaps you can push your finger into the soil a bit, or a lot, if you're so lucky to have a burrowing animal tunneling through your root zone! All of this soil life, burrowing/tunneling activity, and insect activity are positives for our key goals: nutrient availability, reversal of compaction, moisture retention ability of the soil profile, humus formation, and water percolation.
Supplemental Watering
Throughout the summer months (May-August), if you're local area is falling behind on average rainfall, give the whole rootzone 1.5" of water, twice a month. You can measure that setting up a sprinkler, and placing an open evenly shaped container in the zone watching to see how quickly it is reaching 1.5" of water in the container. Tuna cans work great for that or just a rain gauge.
By the end of your first summer, your root zone should not have an O layer thicker than 2". Also un-decomposed organic matter, again, should not be pilled up or in direct contact with the trunk. It would be best to add only shredded leaves each fall, this will ensure quicker breakdown of the leaves, preventing the O Layer from being "too thick" and carbon dense. How thick is too thick? I'm not sure. But the objective isn't to create a compost pile around your tree. Revisit the soil profile picture above. 2" is probably the thickest you want the O layer.
After 7-10 years (Growing seasons)
Keep the root zone protection in place to protect the drip line, and instead of adding tons of carbon and nitrogen rich organic matter, simply add enough tree leaves in the fall to maintain a 2” thick O layer. There's also no need to shred the leaves at this point unless they are being wind swept over the winter.
At this point you can also expand the root zone, to give you're maturing tree more biologically active, non-compacted soil, if you can afford to loose more lawn, the tree will be most appreciative.
Ornamentalizing the Rootzone
Killing the turf grass within the No-Mow/Walk Zone is ideal. We recommend for it to be replaced with a simple short seed mix of Black Eye Susan (Rudbeckia hirta), Purple Coneflower, Wild Bergamot (Monarda fistulosa), Great Blue Lobelia, Foxglove beardtongue (Penstemon digitalis), Golden Alexander, Mistflower (Conoclinium coelestinum), and Virginia Wild Rye. This would be mowed down in the fall, or winter once a year over or under the tree leaves. Their mowed stems, if mowed high enough (3"-4" high), will also help the tree leaves stay in place. It is important the shred the leaves finely the first fall, so that this seed mix can make soil contact over the winter (Fall seeded). If this seed mix is applied overtop or underneath unshredded leaves, it will not germinate well.