It took plants 50 million years to develop roots as we know them today. Everyone knows that roots provide anchorage and access to water and minerals in the soil. But they do far more than that!
The first structure to emerge from a sprouting seed is called the radicle. The radicle becomes the primary root. If the primary root continues to grow and develop, it will have a taproot system. Carrots are a common example. If several smaller roots develop, the plant will have a fibrous root system. There are also aerial roots, buttress roots, and stilt roots! Whatever type of root system your plants have, good soil health and soil structure are critical to plant health.
Root hairs are not actually roots, as we think of them. Root hairs are actually cells used by plants to increase surface area. These threadlike cells push their way through macropores and micropores in the soil, in search of water and nutrients. As actual roots move through the soil, in search of new resources, these root hairs are sheared off.
Root hairs can live for two weeks to two years, depending on the species. Usually, they only live for 2 or 3 weeks, but this is where the majority of water and nutrient absorption takes place. In legumes, this is also where root nodules used in nitrogen fixation develop. The root hairs curl themselves around the bacteria responsible for nitrogen fixation and allow themselves to be ‘infected’ with these beneficial bacteria. New root hairs are constantly being formed at the root tip, behind the root cap.
Tree roots can damage sidewalks, patios, and your home’s foundation, so plan ahead before installing trees and large shrubs. Poor health or branch die off on one side of a tree or large shrub can often be directly linked to damage to the root system from construction, digging, or heat islands. Transplanting and repotting plants often shears off a large number of these root hairs. This is what causes the initial wilting.
We used to think of tree roots as going down, down, down, into the Earth. In some cases, that is accurate. One tree in the Kalahari desert has a root system believed to be over 220 feet deep, but, in most cases, tree roots don’t look anything like that. Tree roots are most easily pictured as a goblet set on top of a dinner plate. The goblet represents the aboveground portion of the tree while the shallow, far-reaching dinner plate represents the root system. Very often, a tree’s root system is 4 to 7 times the diameter of the aboveground portion. Trees are often classified using a ‘root-to-shoot’ ratio. This ratio refers to the weight of the aboveground portion of the tree to its below ground growth. Normally, this ratio is 1:5 to 1:6. This means that the 5,000 lb. tree you see probably has a root system that weighs over 1200 lbs.
The majority of a tree’s root system is found in the top 18 inches of soil. This is why trees fail over when the soil gets waterlogged. Trees growing in heavy clay soil, such as we have here, in the Bay Area, tend to have smaller root systems. This is because clay soil holds far more water and nutrients than other soil types.
Many root crops are edible. These include beets, carrots, radishes, rutabagas, turnips, ginger, turmeric, horseradish, licorice, sassafras, and sweet potatoes. You may think that regular potatoes are a root crop, but they are not. Potatoes are tubers, which means they are the starch storage structures for rhizomes, or underground stems.
Most garden plant root systems are relatively shallow. Rooting depth of garden vegetables can generally be classified as:
What does all this mean?
This means that it can get crowded down there, if you are not careful. If you have deep raised beds, save them for the medium-sized root systems. Most deep-rooted perennials are best planted directly in the ground. The most shallow-rooted plants can often be grown in containers. Root depth also plays a big role in how drought tolerant a plant can be, and how deeply they need to be watered.
When removing plants from your yard or garden, it is best, whenever possible, to cut the plant at ground level and leave the roots in the ground. As the roots decompose, they will feed the local soil microorganisms, which will migrate, over time, to help another plant thrive.
You can grow a surprising amount of food in your own yard. Ask me how!