A few days ago, we were discussing the benefits of permaculture with a friend who had never heard of it. (We can hardly wait until we are able to go take the PDC and Internship permaculture courses in Australia!) John said something that sparked the idea for this article.
Functions of Roots
Absorption. The primary function of many roots is to absorb water and other nutrients from the soil, air, or water in which they reside. Most people think of the large, noticeable roots first, but these roots are storage roots. The roots that absorb nutrients from the soil are the fine, hair-like roots. Altogether, the length of the fine, absorptive roots from one plant can be miles long.
Storage. The large roots are primarily for storage of nutrients, water, and sugars/starches which the plant uses for food. Some of these roots, often tubers or taproots, are used to feed us, such as potatoes, carrots, onions, and parsnips (further clarification below).
Anchorage. Without the roots of viable plants, land will soon become a veritable wasteland. This has happened many times in the history of the world, through overgrazing or improper use of land. Without roots to hold in the rich topsoil, the topsoil is easily washed away. Think about the area that used to called the ‘fertile crescent’. I would’ve loved to see what it looked like 2,000 years ago. Actually, we can, in a way. A lot of the re-greening and land rehabilitation projects are restoring lands in an amazing way. (Here’s a couple of videos for you: Green Gold and Greening the Desert).
It’s not only the soil that washes away when it’s not anchored to the land. Water is lost too. Without roots, the soil is loose and when it rains, it’s easily moved, and the rain and soil run down slopes into streams and end up dumped into the sea. If the soil is anchored by plants’ roots, the soil doesn’t move, and much of the rainfall will sit on top of the soil until it has time to seep deep into the soil. It takes much longer for the water to move through the soil system below ground than it does for it to flow above ground, and the water will slowly flow downward, by gravity, into streams and rivers. With this slowed movement, rainwater can be held in an area for weeks or months, and the rain from wet seasons will likely still be available to plants through dry seasons.
Types of Roots
There are many different types of roots and root words. Here’s a quick run-down of types of roots and their functions.
Adventitious roots: Roots that arise from the stem. Prop, aerial, and stilt roots are all adventitious roots.
Aerating/Breathing/Snorkler roots (Aerenchyma): Roots that rise above the ground, and often above water as well, most commonly being found in swampy or flooded areas. These roots absorb air, allowing the roots to ‘breathe’. Only special plants have adapted to live in swampy conditions, and this is one type of adaptation.
Aerial roots: Roots that are entirely suspended in the air. Epiphytes are plants that grow on other plants (often non-parasitically), and they absorb what they need from rain, air, and debris and dust that gathers around them using aerial roots. Many orchids are epiphytes.
Annuals’ roots: Annuals tend to have shallower root systems, and perennials tend to build much deeper root systems. It’s definitely not always the case. But it’s a good generality. Understanding how deep your plants’ roots are likely to burrow into the soil will help you know how far down your soil needs to be aerated and broken up. For land that will be supporting a garden for the first time, the soil is likely hard and rocky.
You may need to till the soil to break it up, and add as much organic matter as you can get your hands on, whether you buy it or make it yourself. Once your soil is rich and healthy and full of organic matter, it’s a good idea to try to avoid tilling each year because the activity of the millions of organisms in your soil builds pathways and systems and connections… and tilling would only break those connections and likely kill many of the beneficial worms and organisms that you want around in your garden to keep it healthy.
Bulbous roots: The bulbs we think about are generally tulip or onion bulbs. Onion bulbs display the layers that are typical of bulbs. A bulb is actually a small, often underground, bit of stem surrounded by many layers of ‘leaves’ which store food for the plant. Some bulbs are edible (e.g. onions) and others are not (e.g. tulips).
Some plants, including many onions, produce bulbils at the tips of flowering stems, after the plant has flowered (also called bilbels or bulblets). It is basically the ‘seed’ of the plant, just packaged differently than a typical seed. Some bulbs produce little offshoot bulbs (miniature bulbs that form as a side-growth of the bulbs under the ground). These off-shoots (baby bulbs) and the bulbils can be planted and they will grow into new plants.
Contractile roots: These types of roots contract and tighten using a cork-screw or spiraling method. It is thought that this pulls the plant deeper into the ground, anchoring it further and possibly bringing the roots down to a more comfortable temperature level. This happens by the thickening of cells in some areas and constricting them in others to form a spiral, which draws the root in like a spring and exerts a pull on the plant.
Feeder roots: These roots are small and hair-like. They form a dense, tangled network, working their way through practically every square inch of the soil to absorb as much water and nutrients as they can. They may be small, absorbing minuscule amounts of nutrients and water per root, but together they do a lot of work. One thing to consider as well is the amount of fine, organic matter these roots create. If/when the plant dies, these roots can rot down in the soil, adding organic matter to the soil, enriching the soil with nutrients, and becoming food to microbes and worms, as well as creating pathways for water and space for air. The plant is also constantly making new feeder roots as older ones die off.
Fibrous roots: Most people are familiar with taproots and fine-hair roots which form a True Root System. Fibrous roots are different in that instead of one large taproot with many small, hair-like roots branching off of it, fibrous roots are many roots coming directly out of the stem into the ground. This is called a Diffuse Roots System, because there is no dominant primary root. Grasses are the most common formers of fibrous roots. Corn and bamboo, being types of grasses, are probably the most notable examples. Palm trees are another easily-observable example.
Lateral/Side roots: Lateral roots extend horizontally from the primary root, branching out through the soil and anchoring the plant more securely. Lateral roots may be medium-sized roots (smaller than the taproot) or much finer, smaller roots. They may also help take up nutrients and water.
Parasitic roots: A parasitic root is called a haustorium. Mistletoe is probably the best example. The seeds of mistletoe are spread by birds and are sticky, which allows it to stick to the branches of its future host tree. It sends out a haustorium, which burrows into the structure of the branch, connecting itself to the tissues of its host tree, and extracting nutrients and water from the host tree. Mistletoe doesn’t need an ounce of soil around its roots in order to grow and thrive. It steals everything it needs to grow.
Pegs: Peanuts are a ground nut, but they do not grow on the roots of the plant like many people think. A peg grows up from the stem of the peanut plant, and hooks back down where it buries itself in the soil, and the peanuts grow underground on the peg. It’s not a root or a stolon. It’s more like a buried flower.
Perennials’ roots: Perennials generally form deeper and stronger roots systems than annuals do. This isn’t always true, as seen in the case of large trees in the rainforest which form relatively shallow roots systems.
Primary root (radicle): This is the first root that the seed sends out. It often develops into a tap root in a true root system.
Primary root growth: Growth that lengthens the roots (vs. thickening it).
Propagative/Sucker roots: Roots that spread under the ground by forming buds off of the main roots that can send up growth that becomes new plants. Plants in the mint family are notorious for doing this, as are aspens, which have created the largest organism anywhere due to suckering. The alpine forests in the rockies can consist of thousands or millions of acres of aspens, all linked underground in their roots systems, making them, in effect, a single organism.
Prop roots: These are roots that make their way through the wall of the stem above ground, and then push downward into the soil. They help to anchor the plant. Corn and lemon grass are examples of plants that grow prop roots.
Root bound: These are roots from plants that are grown in small pots for too long, which causes the roots begin growing sideways, around the walls of the pot. This does not make for healthy transplants.
Root crops: This refers to underground plant parts that can be used for food, whether it’s technically a stem (potato tubers), leaves (onion bulbs) or roots (carrots). Some other examples of root crops include parsnips, radishes, salsify, sweet poatoes, rutabagas, turnips, yam, horseradish, lotus, and cassava.
Root stocks: Plants that exhibit certain growth characteristics that can become rootstocks for plants in the same species (and occasionally, the same genus). For example, apple trees that exhibit slow-growing root systems are used as dwarfing rootstocks for apple trees that produce delicious apples but grow too tall, because the canopy of a tree generally grows in relation to the growth of the roots. The process is done by grafting a cutting (the scion) of one apple tree with the stump of another tree (the rootstock). The new graft will grow together and the tree will produce the fruit of the scion but grow with the characteristics of the rootstock. Rootstocks are most often used for grafting in fruit trees (apples, peaches, plums, all sorts of citrus, etc.), but is also done with shrubs, bushes, and some vegetables.
Secondary root growth: The thickening of roots (vs. the lengthening, which happens in primary growth).
Stolons: An above-ground shoot that can grow new roots and become a new plant. Strawberries are well-known for spreading by stolons.
Storage roots: Roots that can store sugars, starches, water, and nutrients for future use by the plant. Tap roots are storage roots, as are some lateral roots.
Strangler roots: There are some fig trees that can grow epiphytically at first, with its roots entirely in the air as it is perched on another tree.
Eventually it will grow roots long enough to reach down do the soil. As it grows more and more of these long roots, it literally strangles and chokes the host tree on which it sits, competing for air, water, and sunlight. It’s not parasitic in the sense that it takes nutrients directly from its host plant, but it out-competes it. These type of plants can also settle on rocks and send their roots outward into soil many feet away… in which case they wouldn’t be strangling another plant in their quest to grow.
Support/Buttress roots: Roots that grow above ground to add greater support to the plant, often a tree. They may only grow a few inches above ground, or they may extend upwards from the ground to 5 or more feet!
Surface roots: Roots that grow outward at or near the surface of the soil, taking advantage of the greater abundance of nutrients and water that often exist on the surface of the soil.
Taproots: The longest, thickest root sent straight downward from the stem, in a true root system. It becomes a storage and anchorage root. In some plants, it is edible (e.g. carrots or parsnips).
Tree Roots: Some trees send roots deep into the earth. Others actually form relatively shallow roots systems, like many pine trees. If you want a strong, sturdy, stable tree that is much less likely to get blown over in the wind, pick deep-rooted, hard wood trees like oaks or some maples.
Tuberous/Tuberoid roots: Roots or other plant parts (like the potato, which is technically a stem) that has become enlarged in order to store sugars, starches, water, & nutrients for the plant.
Water roots: Roots that live entirely underwater, like the roots of water lilies and lotus. These roots are still able to “breathe” air because the lily pads that sit on top of the water pull in air and pump it down to the roots below.