When leaves turn color and drop to the ground in fall, they’re going dormant. We think of them as going to sleep. But unless the soil is frozen solid—something that doesn’t happen here in western Nevada County—trees and shrubs stay busy. Their roots are out searching for nutrients to prepare for the burst of growth in spring and on into summer.
Roots grow further outward and more shallowly than you’d probably think. They can extend well beyond the canopy, with most of them only 6-24 in. below the soil surface. Each year young feeder roots grow through the winter searching for nutrients and water. They send them back to the larger older roots to be stored.
Once spring comes the stored nutrients are tapped into. First for flower and fruit production, next for leaves, then stem and trunk, and lastly the roots.
This root growth should determine where we plant new trees, how we plant them, and how we care for them
Different types of plants need different types of soil nutrients. It gets down to soil organisms because the roots of some plants make use of different soil organisms, or microbes, than other types. We want to allow the right microbes to flourish for the plants we want to grow.
For example, lawns and trees don’t mix well. They each need different treatment and they foster different microbes. Lawns usually get what they need at the expense of the trees’ needs. Keep them separate.
It’s a great time to plant trees and shrubs
Because of this active root growth and our mild winters, fall and winter are great times to plant trees and shrubs. Science shows the right way to plant, and some of it goes against common wisdom. To plant and set your plants up for long term success and good anchoring, follow these planting steps:
- Dig the hole 2-5 times as wide as the root ball from the nursery container, bare roots, or a balled and burlaped roots. Keep the hole only as deep as the root ball; you want the topmost roots to be at the surface.
- Check the plant for circling roots, pull larger ones away and straighten them. Adjust the hole width if necessary to accommodate them. For small circling roots, cut across some and straighten out what you can.
- Score the sides of the hole with a spading fork, pickaxe, or shovel to create a rough surface for roots to grow into.
- Backfill the hole with the native soil from the hole, and only organic fertilizer mixed in. Do not add amendment (you’ll do something else), because the difference in texture and nutrients between the soil in the hole and that beyond can encourage roots to remain in the hole and possibly become rootbound. This doesn’t anchor the tree well enough, and the roots may not go out to find nutrients. Do not tamp the soil, simply water it to settle it and remove air pockets.
- Apply mulch about 3 inches from the trunk out to the canopy edge and a little further, about 3 inches deep (but see below for fire safety). This can be compost, fallen leaves, or wood chips from local arborists. If your soil is poor, start with compost or bagged composted forest products that contain other nutrient materials. Later, cover that with wood chips. Roots need the right temperatures and mulch protects them from heat damage. As mulch breaks down it supplies the soil with nutrients.
More on mulches
Using leaves can add to fire risk, so save them for the least risky areas. It’s sad, because they’re nature’s method of adding and recycling nutrients. You can save them for cold composting to use when they’re fairly broken down.
Wood chips have been shown to pose the second lowest fire risk next to rock mulch. See Mulch to Save Water—But What about Flammability? for more detail.
Start with an inch or two and add more each year for best fire safety.
If the soil around the tree or shrub is very compacted, take a spading fork and sink it into the soil in spots concentrically around the tree and wiggle it back and forth to make some holes. Move outward to just beyond the canopy of the tree. Proceed with adding mulch, and organic fertilizer if deemed. Do this for new and for struggling established trees.
Rain will sink into the ground more readily and soil will stay moister with mulch on it. But if winter rains fail to provide enough, water the trees and shrubs so they don’t dry out their first winter or two.
Feed trees and shrubs in fall and winter, if they need it, with organic fertilizers, after their leaves have dropped. Do this for evergreens, too, because their growth is slowed.
Why use organic fertilizers?
Organic fertilizers require soil organisms to break them down. They’ll get incorporated into the soil ecosystem and the roots can access them as they need them.
Soil biology is very complex and evolved over millennia. Roots create the right conditions for which soil microbes will grow and make the right nutrients they need. If you add chemical fertilizer to the soil, the roots take that in instead, and stop fostering the growth of the right microbes. This leaves the plant requiring a steady supply of fertilizer.
One of the most significant resources for roots is mycorrhizae, the filamentous roots from fungi (those mushrooms that pop up after the rains). They mostly spread from tree to tree to set up a symbiotic relationship with the roots of most plants. They connect with the roots and reach much farther out from the tree to mine for minerals, like phosphorous, and water. And they send these back to the tree roots and in return they get carbohydrates from the plants.
Mycorrhizae are present in all but the most damaged soils. But when we use chemical fertilizers, we break that beautiful, essential connection. The mycorrhizae are killed off in the process.
Work with nature’s wisdom
So let the roots do what they know how to do and support them in that. We don’t need to control them; we don’t want to love them to death. They’re working now even when it looks like they’re going to sleep. Understand them and appreciate their beauty.
Related Reading
Two Powerful Ways Soil Soaks Up Carbon Dioxide
It’s Getting Hot! There’s a Surprising Solution to Global Warming