PHOTO: Guillaume Delebarre/Flickr
Karen Lanier
September 18, 2017

Fall is a great time to plant perennials. When you do, be mindful of the roots. A lot happens in that mysterious, underground network. Roots are crucial components of plants, similar to brains. Imagine planting a human upside down. The brain goes into the ground, holds the memories, calculates the timing and directs the functions of the rest of the body. Roots are one of five organs of the plant body, the others being leaves, stems, flowers and fruit.

Fall-Planted Roots Have It Good

Spring-planted roots might be shocked a little, trying to warm up in the chilly ground. They’ll grow slowly. However, in the fall, the soil has warmed all summer, so roots are cozy and get to stretch out with ease. Even though it looks like nothing is happening above ground, continue watering regularly so the roots can easily get established. Don’t worry about frosty mornings. The roots will continue growing until the soil freezes solid. Add mulch to the perennials after they die back from a hard freeze, so that there’s less thawing and refreezing. Frost heaving can force roots back up to the surface. The best time to plant fall perennials is about a month before the freeze hits, so the roots can stake their claim.

During the winter, most roots go into a state of dormancy, resting and minimizing their basic life-sustaining processes. Like a bear coming out of hibernation temporarily when the temperatures rise, if the ground gets warmer than 32 degrees F, roots become active again. It doesn’t matter if above-ground temperatures are brutally cold and no sign of life emerges on the stalks; without leaves to photosynthesize and make food, the roots live off stored sugars. This ability of roots to sustain life year-round benefits the entire plant. When spring arrives, it is prepared to send energy back out to the extremities for budburst.

Roots Communicate Among Plants

In the book, The Hidden Life of Trees, Peter Wohlleben shares forestry research revealing that subtle messages go between roots throughout plant communities. Root tips send and receive electrical signals that warn of threats and alert other plants to prepare their defenses, and not just among their own kind. Trees “talk” to shrubs as well as grasses and flowers in the wild; all share information for their collective survival.

Farm fields lack the native, natural language of the forest, says Wohlleben: “Thanks to selective breeding, our cultivated plants have, for the most part, lost their ability to communicate above or below ground—you could say they are deaf and dumb—and therefore they are easy prey for insect pests. That is one reason why modern agriculture uses so many pesticides. Perhaps farmers can learn from the forests and breed a little more wildness back into their grain and potatoes so that they’ll be more talkative in the future.”

Roots & Timing

Plants budget their resources, and not all processes can be fully supported at once. For every season, a different part of the plant is primarily engaged in its specialty. For roots, their glory days are autumn and winter. Even more so for plants we put in the ground in the fall, perennials that will put their energy resources into getting their roots established before directing attention to reproduction.

Since last spring, the roots of established trees have been sending water up the stalk or trunk, through the branches or stems, and into the leaves. As the days grow shorter, the water and food supplies lessen, and the special layer of cells at the base of each leaf toughen up. Called an abscission layer, it slows and finally blocks nutrients from passing to and from the leaves, and they lose their chlorophyll. The green goes away and allows the other pigments to have their moment.

Understand Roots’ Primary Functions

1. Anchor

Some plants have more of a tap root than others, yet plant size is not a clue to the underground anchor. Some native grasses are rooted six or more feet down. However, the tap root isn’t very common in established trees. It grows downward to provide anchorage at first but is soon taken over by other roots or meets obstacles that divert its path. Roots extend laterally and need their own habitat: water, oxygen and space sufficient for thriving. Without obstacles or competition, tree roots could spread an extensive network two or three times the radius of the tree’s crown.

2. Store

Photosynthesis in the chlorophyll of leaves creates carbohydrates. Most of these are stored closer to the source (in stems and stalks), and some carbohydrates move down into the roots for storage. The stored energy is exerted in spring, unfurling tender leaflets and pushing forth flower buds.

3. Conduct

Through osmosis, water moves into and out of the roots. This means that the water will move to the areas of lowest concentration, whether it be down in the ground or up in the treetops. In a sense, your plants could be watering the soil, especially if excessive fertilizer or de-icing salts have raised the salt content in the soil.

4. Absorb

The large, branching roots do the first three functions—anchor, store and conduct—but only the fine, hair-like roots absorb water and minerals. Most of the absorbing, feeder roots of a tree are found in the first foot of soil. Absorbing roots often depend on fungi in the soil, mycorrhizae that form a symbiotic relationship. The fungi aid the roots in absorption and receive nourishment from the roots that provide their subterranean home.

Reminders For Healthy Tree Roots

Remember that new plants put energy into establishing roots, so make sure your soil is loose enough for those roots to find their way around. When you put a transplant in the ground, don’t cover up the root crown, the area where the main roots join the plant stem, also known as the root collar or trunk flare. Don’t let dirt or mulch pile up and cover it.

Poor planting techniques can cause girdling. Roots can grow across or around the stem or other roots and choke them, constricting the movement of phloem (the vascular system of the tree). Because the problem typically develops underground, it is difficult to diagnose. Often in urban areas, development, construction and heavy vehicles compact soil and damage the habitat that absorbing roots need. One symptom to watch for is early fall color. If you suspect an established tree has roots that are suffering, contact an ISA certified arborist to assess the damage and find a solution.

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