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)
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 4-6" 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 4-6" application should look like a 2-3" 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 benefical 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 4-5" layer somewhat loosely laid, perhaps 2-3" 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 to the right: 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
After the first growing season
Supplemental WateringThroughout 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.
After 7-10 years (Growing seasons)
Ornamentalizing the Root Zone
Above is the wild native sunflower, that was cultivated into the plants that occupy the sunflower fields we know and love. When you grow the wild uncultivated Helianthus annus - Annual sunflower, they bloom with more heads per plant, and smaller heads with brownish centers. Using weakly rooted perennials and native annuals may enhance the soil biology within the Root zone, through the addition of plant diversity. Using only native plants maximizes diversity in fungal, bacterial, and insect interactions with the plant through evolution-based established relationships. Once again, bio-mimicry is almost always the best solution because nature is perfect like that.
If you decide to help your tree breathe easy, and grow vigorously using these Root Zone Management techniques please email Pioneerlandscapesllc@gmail.com so we can exchange information and hopefully exchange success stories/pictures.