Tree planting season in Austin runs from mid-October through early-March, depending on the temperatures of the Fall and Winter. That means tree planting projects with APF generally fall between our city-wide volunteer days, and we rely heavily on individual volunteer work days to help us accomplish the planting goals of our Future Forest Project.
The Future Forest Project (FFP) is an intensive, five-year program designed to increase the number of trees planted on public land, and develop more efficient strategies for deploying volunteers. The three target areas of this project are:
- Natural Woodlands and Nature Preserves
- Riparian Corridors
- High-use Parklands
In each of these areas our goals are to regenerate forests, remove invasive species, plant trees, seedlings and saplings, add irrigation where required, and provide care to the new and extant trees and soils at their root zones, mainly in the forms of pruning, root collar clearing, and mulching. Though we will be using these strategies on public lands, they are just as useful for trees on your personal property, and many are very easy to complete with just a little training. Two of the most important things you can do for your trees are also two of the simplest – root collar clearing, and mulching. Read on to learn the basics, and if you’re interested in helping us care for Austin’s trees – email us now to set up your volunteer work day!
Root Collar Clearing 101
Our friends at Urban Forestry have put together a comprehensive Root Collar Clearing 101 guide that you can view here, but here are the basics:
What is the root collar?
The root collar, also called the root flare or trunk flare, has been described as the heart of the tree – it is the area where the trunk meets the major lateral roots. The root collar should always be visible, however, it is sometimes buried or covered by mulch and soil. Simple steps at the time of planting can help prevent the problem, but root collar clearing is an important maintenance practice for young and established trees alike.
Why is it important to keep the root collar clear?
The root collar is a transition zone between the trunk and the roots, and is technically part of the tree’s trunk. Unlike roots, the trunk is not specialized to resist constant soil moisture. That means excess soil and mulch at the root collar can trap moisture against the bark of the root collar and encourage bark decay. This decay restricts the flow of oxygen and carbon dioxide in and out of the phloem (inner bark), and over time the lack of air can kill phloem cells and interfere with the downward movement of food (photosynthate) to the roots. Without nutrients and air, root growth is stunted leading to the tree’s decline or death. Additionally, a buried root collar may allow adventitious roots, and soon girdling roots, to grow from the trunk. These excess roots inhibit the proper function of the vascular system of the tree, exacerbating the tree’s health issues.
How do I clear the root collar?
1) Use hand tools to carefully clear soil, mulch and vegetation from the trunk, avoid wounding the trunk tissue
2) Monitor the root collar every few months for vegetation re-growth, excess soil and mulch, and look for any new adventitious or girdling roots
How does the root collar get buried?
Root collars can be compromised through a variety of common circumstances. Here are just a few:
- Grade changes during landscaping projects bury the once clear collar
- Inappropriate nursery practices allow the collar to be buried and saplings arrive already compromised
- Trees are planted too deeply, or may gradually settle in the planting hole
- Over time, soil and mulch break down and migrate into the well of a mulch ring
- Mulch is misapplied against the trunk
- Excessive mulch is applied and may lead to death of the root collar
How do I know the root collar needs clearing?
There are a couple of easy things to look for when you are considering a root-collar clearing project:
1) You should always be able to see the root collar, be sure there is a mulch-, and vegetation-free zone around the root collar
2) If you observe girdling (circling) or adventitious roots (root sprouting from the trunk), on a tree in your park, request a site visit by PARD or Urban Forestry and they will prune when and if appropriate. For trees of your own, contact an arborist to assess the issue.
Mulching is one of the most important, and easiest!, things you can do to ensure the health of your trees. Below are the basics of mulching, as well as a short video from our friends at Urban Forestry and GrowGreen Austin that will give you a few more handy tips.
What is Mulch?
Mulch is material you cover the soil with after planting to reduce run-off, protect roots aand keep down weeds. Mulch can be organic (pine straw, bark, etc.) or inorganic (white rock, lava rock, recycled rubber, etc.)
When Is a Good Time to Mulch?
There’s practically no bad time to mulch here in Austin. In late fall we mulch trees that have been recently planted, or trees that may not be completely cold-hardy for the upcoming winter. However, you can mulch any time!
How Much Mulch Should I Put Down?
Can you mulch too much? Yes, you can. You’ll want to apply a layer no more than 2 inches deep. Don’t put down new mulch until the old mulch has mostly decomposed. Don’t pile up mulch around trees like a “mulch volcano.” It’s bad for several reasons. Tree roots can grow into the mulch instead of the soil, making the tree less drought-resistant. Bugs can hide in the mulch and bore into the trun, and the mulch can trap excess moisture against the trunk, encouraging decay. Mulch volcanoes also reduce the oxygen supply to roots, while aiding harmful soil microbes that produce toxins. Mulch should never touch the trunk of a tree or shrub.
How far out should the mulch go?
Make a ring around the tree as large as the tree’s canopy. This is called the drip line, and many of the fine, water-gathering roots are concentrated on the outer edges of the tree’s root system. These generally extend as far out as the tree’s longest branches.
Want to learn more or lend a hand?
If you’re interested in learning more about tree care, and other park improvement topics, join us for one of our PIES educational workshops. Or, if you are ready to get your hands dirty, check out our city-wide volunteer days under the Signature Events heading above! You can also organize your own park project and access our tools warehouse by emailing our Volunteer Manager today!