How Plants Work | The Science Behind Plants

Understanding how plants work has been one of the most liberating experiences of my gardening profession and avocation.

While I will always remain curious, especially when it comes to plants, I will never know it all. Nor do I want to. What’s the fun in that?

However, having a sound basis from which to draw for determining cause and effect has allowed me to have a beautiful landscape and garden, all organic, and with minimal intervention on my part to keep it so.

Author of How Plants Work with The Garden Professors

Linda Chalker-Scott flanked by fellow “Garden Professors” Holly Scoggins, Jeff Gillman, and Bert Cregg (L-R),

Fortunately, we have people like Linda Chalker-Scott, Ph. D, to help us understand how plants work.

In this podcast, we touch on a few of the subjects she addresses in her book, How Plants Work; the science behind the amazing things plants do.

As an Associate Professor of Horticulture and extension urban horticulturist at Washington State University, her science-based approach to all she writes and talks about is one of the qualities I love most about her.

Roots & Fungi: An Important Relationship

The relationship that roots have with beneficial bacteria and fungi, especially mycorrhizae, has convinced Linda that we should never, ever, use fungicides in our soil. Fortunately, home gardeners rarely need to resort to this for vegetable and ornamental gardens.

However, lawns often succumb to fungal diseases. We all too quickly reach for a chemical solution to the problem. While it may resolve the issue for which a fungicide is applied, what’s not seen is that the more-important beneficial fungal life below the soil is destroyed as well.

One of the most beneficial fungi we talk about today because of the symbiotic relationship it forms with the roots of plants is mycorrhizae. It’s naturally present in healthy soil. The fungi attach to plant roots to extract nutrients. In return, the mycorrhizae fungus adds a vast network of thin root extensions to help draw in more nutrients and water to the plant.

One of the biggest inhibitors to mycorrhizae’s ability to benefit plant roots is excess phosphorus and salt-based synthetic fertilizers.

The bottom line is that the healthier the soil, the more abundance of mycorrhizae and the benefit it provides to aiding plant nutrient and water uptake.

The Primary Ways Plants Defend Themselves

Plants work in mysterious ways. Because they are immobile and unable to escape predators, they have built-in defense mechanisms that can be remarkably effective.

One of the ways plants defend themselves is with compounds that are poisonous to many insects. The milkweed seen here is one such plant. Monarch caterpillars are undeterred as it is their sole food source.

Poisons – The toxins in certain plants mean that many insects cannot feed on them. An exception is the monarch caterpillar. By ingesting the poison when feeding on the leaves, it makes the caterpillar less attractive to predators.

Repellants – Plants can emit scents that are found to be unattractive to certain pests. It works in a way that prevents any damage to the plant.

Deterrents – Plants that act as deterrents may allow minor damage to plants, but it’s the unpleasant experience encountered by pest insects that help to deter them from causing further damage.

Ethylene gas is a common emission by plants under stress. Some insects are drawn to this and attack the plant. Other predatory insects respond to the same emissions, knowing that prey insects have been drawn to the same plant because of the gas emissions.

Understanding the Breadth of the Root Zone

We often hear about roots extending out to the dripline, or edge of the tree canopy. But that’s just part of the story. The typical root system reaches far beyond the dripline, often 2-3 times beyond, if it can.

The depth of roots depends heavily on the soil. Shallow root zones are common in compacted or disturbed soil. However, in undisturbed, well-drained soil, roots can extend very deeply.

Water, nutrients, and oxygen are the three key needs of roots. The amount available and access to each are the determining factors on the growth of expansiveness of the root zone.

Of the three key needs, oxygen is the primary determinate of how deep roots will grow. The more available the oxygen deeper into the soil, the more likely roots will follow.

Remove Soil From Containerized Plants

Removing the soil medium from plants and trees before planting is counterintuitive. It flies in the face of what we’ve been taught for years. Best practices suggest we do just that.

Roots grow out as far as they can. But in a container, they become bound and can’t fix themselves. Therefore, we have to change the confirmation of the root pattern before planting.

The media in a container is often soilless and not the media we want to introduce to the native soil. Because it’s different, roots tend to stay around it and fail to explore beyond it.

The goal at planting is to get roots growing in native soil as early as possible.

A good alternative is to buy bare root plants. While bare root trees and shrubs are typically smaller and may take a little while longer to establish, once they do, they will take off and ultimately establish in a more sustainable environment. That usually happens by the third year.

The Wiggle Test

A good way to know if your tree is establishing below ground is the “wiggle test.” Every month or so, lightly wiggle the trunk. Over time, you will find it becomes stiffer. That is the best indication that roots are settling in and the plant is alive and well.

Staking trees is an often unnecessary practice that can make the tree weaker. An added consequence is damage to trunk and limbs when support wires are left on too long.

Staking trees inhibits trees from establishing. It’s a practice that should be avoided whenever possible. Allowing a tree to move with the wind makes it stronger and quicker to establish.

If you find that staking is required, be sure to remove the supports within a few months to minimize damage to the tree and bark.

Does Flower Color Deter Certain Pests?

In a recent observation, Linda noticed some flowers on a certain plant were untouched while others were destroyed. In this case, the white flowers were decimated while the pink flowers were untouched.

The working theory is that flowers of darker color may be unpalatable because of heavy metals bound by the pigments responsible for the color. The soil pH also plays a role in binding potentially unattractive ingredients for pests to consume.

Mulch Volcanoes – Not as Bad as We Thought

Mulch volcanoes piled high around tree trunks has been the source of controversy for years. New research now refutes many of those concerns when using appropriately sized mulch.

Most of us would agree, mulch volcanoes look horrible and get a bad rap. But, is it truly that bad? Perhaps not. Does the mulch cover the sins of poor planting? Does the mulch hurt trees?

New research yet to be published shows the mulch doesn’t harm trees but can actually help trunk wounds heal faster vs. when exposed.

Arguments for not creating mulch volcanoes is the excessive depth of the mulch and contact of the mulch with the tree trunk. However, the main problem appears to be in the type of mulch used.

Finely textured mulch is harder for moisture and air to penetrate. Coarse, chunky mulch has proven to offer great water and gas transfer.

In separate studies, deep layers of a coarse woodchip mulch suppress weeds while not harming soil in any way. The key is coarse mulch and texture vs. finely textured deep mulches.

So while volcano mulching may not be bad, the choice of mulch appears to be the real problem.

How Plants Tell Time

Trees start preparing for winter long before we notice a change. As nights become longer, they begin biological processes that help them prepare for fall and winter by measuring the ratio between light and dark.

As day length shortens and temperatures become low enough, trees show their change. But it’s a two-part process. Unlike temperature, the decreasing amount of daylight beyond the summer solstice is the most reliable clock trees use to begin their fall and winter preparation.

There’s one exception: urban trees. Due to artificial light, a tree can be tricked to think it’s still summertime because the artificial light masks the fact that days are growing shorter.

Seeds That Need Light to Germinate

Small seeds tend to be photo dormant. They must have light to germinate. As we till, new weeds germinate because they are brought to the soil surface, and light triggers germination.

Mulch works well to keep light away from new seeds brought to the surface.