Roots – the most important factor for healthy plant growth


When otherwise well cared for plants start to develop signs of wilting, it’s often caused by an unhealthy root system.  There is a reason why people say “The root of the problem.” A plant’s health depends on the correct balance and function of all of its parts, but the roots play arguably the most important role. 

Why are roots so important for plant health?

  1. They absorb water, minerals, and nitrogenous compounds from the soil to sustain the plant
  2. The roots act as a conduit to transport the water and nutrients to the leaves
  3. Roots provide storage for food
  4. Roots anchor the plant to the ground

This is demonstrated by observing repeatedly defoliated plants; some of the roots die back as a result. Defoliation is when the leaves are removed from the plant.  Equally, if a section of the root system is destroyed, some leaves and branches will die off.  We often forget about the roots because we don’t see them.  The whole time they are doing their job well. We don’t give them a thought, working away underground, out of sight, and out of mind. However, roots have an essential role to play in the growth and welfare of the plant

The 4 Main functions of the root system

Absorbing water and minerals

The roots have thin-walled epidermal cells and hairs designed to absorb water and dissolved minerals from the soil.

Many plant roots also have a symbiotic mycorrhizal relationship with fungi, which allows for greater absorption of nutrients as the fungi colonize the plant host’s root system. This provides an increase in water and nutrient absorption capabilities for the plant.  While, in turn, the plant provides the fungus with carbohydrates formed from photosynthesis.

The nitrogen the plant needs is usually fixed by bacteria and single-celled organisms called archaea that live in the soil. The roots of some plants can convert nitrogen from the air; for example, some tree species have roots that grow partly above the soil’s surface.


As a Conduit

When nutrient-rich water enters the root from the soil, it uses a system called osmosis.  The xylem vessels located in the middle of the root transport the water, taking it up through the stem to the plant’s leaves.

Photosynthesis is essential for plants to grow and survive. Without the water and nutrients drawn up by the roots, Photosynthesis cannot occur.


Food Storage

Many plants store food in their roots, especially those with taproots.

Generally, perennial plants need to store enough food to get through the winter to have sufficient energy to grow in the spring. It is this storage system that we consume when we enjoy root vegetables.  The vegetables we eat from below the ground are those that are particularly efficient at storing food reserves.  Examples of foods are carrots, parsnips, potatoes, and radishes.


Roots Anchor

Sometimes roots travel deep into the soil, but most cases the start to travel horizontally not far below the surface.  Tree roots will always follow the course of least resistance and to the easiest place to obtain water.  It is quite normal for the roots of a tree to cover a distance significantly larger than the spread of the branches that we see above the ground.  Taproots grow downwards and anchor the plant in place.  Some plants have roots that spread out in a network of fine roots close to the surface, and it is the extent of the fine roots that form a mesh to anchor the plant. Roots are separeted in different types according to the way they grow. Let’s have a look at the most common root types, to understand how they work.


The 4 main root types of plants

Common plant roots usually are separated into 3 distinct root types. They are called Taproot, Tubers, Fibrous, and Adventitious.

The type of root a plant has determines it’s adaptive ability to the environment.



Photo by Rasbak // CC 3.0


A taproot system is when there is one main root that is larger and faster-growing than the other roots. Sometimes a plant will produce more than one tap root, but the system is the same. The taproot is the first root that emerges from the seed.  In a taproot system, the secondary roots come from the taproot, and these, in turn, produce smaller lateral roots.  Therefore the taproot is the primary root, the secondary root is called lateral roots, and the smaller roots are known as tertiary roots.

Many plants in cold regions have taproots that enable them to reach down below the frozen surface to obtain water and nutrients.



Tubers develop from elongated stem tissue.  Potatoes are tubers and can be identified by how they grow from the underground stems and have nodes. 

Taproots and tubers are completely different.  Taproots do not have nodes.  It is best to think of them as different parts of the plant.  A tuber is actually an engorged modified, underground part of the stem.

The easiest way to tell them apart is to have a look at them. Tubers have nodes and tend to spread horizontally just below the soil or at the soil surface.  There is usually more than one; their purpose is to collect and hold nutrients.

Tubers grow on underground rhizomes that run horizontally just below the soil or at the soil surface. The tuber itself is simply a swollen section of these rhizomes. Nutrients collect in these swollen chunks. Their purpose is to store nutrients for the plants in order to generate healthy new growth each spring.



Photo by Forestryimages // CC 3.0


In plants that don’t adopt the taproot system, the initial taproot is soon joined by further roots that quickly equal or exceed the primary root’s size so that there is no single defined taproot.  The fibrous root system is when all the roots are about the same size and is a characteristic of grasses.  The roots are shallower than tap root system plants; they tend to be concentrated nearer to the soil’s surface.  Fibrous roots form an extensive root system of fine roots.



 I call these “adventurous roots – they are daring to be different!”

Adventitious roots form on other parts of the plant other than the roots.  The Ficus tree produces adventitious aerial roots that originate from the tree’s branches, and they are a prime example of adventitious roots.  Another useful example is mangroves, where stilt roots grow from the main stem of trees, bending downwards towards the soil.


Benefits of the Different Root Systems

Photo by Aaron Escobar // CC 2.0


Plants have adapted to the geology and geographical aspects of the places they grow.  Of course, we change that by growing them in our gardens, planters, and even indoors.  Plants have established the way their roots grow over millions of years.  So it is likely that the changes we make to the environment they are grown in create modifications that are so subtle we don’t notice them. 

Advantages for Plants with Taproots

Plants with deep taproots can reach water much further down, making them better able to resist drought and frost.

Many plants with taproots are taller plants such as trees and the taproot digging deep down into the substrate works to prevent the tree from being blown over during windy weather.

Taproots also work to secure plants that grow on sand dunes and shifting soil, by anchoring them lower to counteract the shifts at the surface.  Often, they can find good purchase further down.

Taproots are a good place for the plant to store food that can be utilized by the plant when required to create healthy stalk re-growth or seeds.

As previously mentioned, of course, this food storage facility makes them advantageous for us as healthy foods.  Many root vegetables are taproots.


Advantages for Plants with Fibrous Roots

One of the advantages of the fibrous root system is that the plant can take advantage of water close to the surface.  They tend to spread out and obtain water from a wider area and can take up the water quickly.  Advantageous in warm locations where the water evaporates quickly or is in short supply.  It also helps the plant to compete against other plants for the available water.

From our perspective, an advantage is that this type of root system holds the soil in place.  Think of grass on banks that frequently hold the substrate together. Where there is no grass, mudslides become more frequent.


Advantages for Plants with Adventitious Roots

Adventitious roots can be a stress reaction.  When a plant is stressed, they sometimes put out adventitious roots, for example, when the roots are subjected to heavy metal deposits that impact the nutrient uptake.

Another situation when a plant puts out adventitious roots is when the plant has been wounded. For example, we have cut a stem for the flowers or a branch has snapped off in high winds; these injuries induce stem roots to grow in the damaged area.  Growing the extra root in this way gives the plant an additional chance of survival.

A typical reason for plants to put out adventitious roots is as a reaction to flooding.  When the plant roots are subjected to prolonged flooding, they become stressed and cannot take up the nutrients required for the plant’s health.  The adventitious roots facilitate water and nutrient uptake when the main roots are waterlogged.

This is where it gets interesting; flood-induced adventitious root production is utilized for producing major global foodstuffs such as rice and corn.  There is a fascinating article about it from 2016 at

Another way that adventitious roots work for us is in propagation.  Both taking cuttings and grafting depend on prosperous adventitious root growth for success.


You have to Dig it

The taproot system occupies more area than the fibrous roots.  Despite what’s already been said about the path of least resistance, they tend to travel vertically to reach deep into the substrate.  Fibrous roots may initially look like there is more root, but it is all close to the surface and easier to find.

This shows that when you dig up a plant to examine the roots, it should quickly become apparent that the fibrous roots are close to the surface.  Meanwhile, the taproot plants are anchored into the ground by the root system secured by the single (occasionally double) primary root. It may not be apparent at first that you are looking at a taproot system because, especially when water is plentiful at the surface, the taproot plant will send out horizontal lateral and tertiary roots close to the surface.


Vegetables by Root Type

Root VegetablesFibrous Rooted VegetablesTubers and Others
CabbageCorn and adventitiousPotato
CarrotPak Choi 
ChardRice and adventitious 
Sweet Potato(tuberous root)  

Tomatoes grown from seed have a taproot system; those grown from cuttings will develop a fibrous root system.

It may be surprising the wide variety of vegetables that we use that are taproot plants.  Isn’t it fascinating that something like Rosemary can grow to quite a substantial shrubby bush on fibrous roots?  The critical thing to remember, whatever the root type, is that our plants’ roots are vital to their health and well-being.  Any sorry-looking plants could have a problem at the roots; the most common problem is root rot.


Root Rot

Root rot is a problem that occurs in plants growing in wet soil.  The cause is due to a fungus, the most common ones being:

  • Honey Fungus (Armillaria)
  • Phytophthora
  • Phythium
  • Rhizoctonia
  • Thielaviopsis

One of the problems with identifying these root rots is that you can initially mistake them for something else, including lack of water and nutrients.

If you dig up a plant with any type of root rot, you will discover brown roots that are soft instead of firm and white.


Honey Fungus

The name honey fungus covers several different fungus armillaria species that attack and kill roots of woody and herbaceous perennial plants. You can identify the problem by observing the decaying roots and by white fungus between the bark and wood.  The initial symptoms are small, pale leaves, frequently premature autumn color, failure to flower when expected, and cracking and bleeding at the stem’s base.

The only treatment is to remove and burn the plant.  Also, by not planting anything else in its place that may be susceptible as the fungus rhizomorphs will still be present.



Photo by Liberato, JR // CC by 3.0


The most common cause of root rot after Honey Fungus is Phytophthora. It affects a wide range of trees and shrubs, bedding plants, pot plants, herbaceous perennials, and even bulbs on occasions.  It is primarily a disease of waterlogged soils or heavy soils, and you can easily mistake initial symptoms for waterlogging only.

The main symptoms are wilting, yellow or sparse foliage, and dieback of the branches.  These do not show until the decay is already advanced.  The symptoms are not restricted to phytophthora, except in conifers when there is a gradual fading of the color’s vibrancy, to dull green, then a grey tinge, and finally, they are all brown.

Inspection of the roots of an infected plant will show that the root system looks unhealthy, with clear signs of decay, and the fine feeder roots will have rotted away.  Because there is no other visible sign of phytophthora, the only way to be certain was the cause and not “just” waterlogging by sending a sample for laboratory analysis.

The only treatment is to destroy the plant, and the soil from the whole root area is replaced.  Again, don’t be tempted to plant anything else that may be susceptible in the location of a suspected phytophthora problem.



Pythium is a group of destructive root parasites of the Pythiaceae family.  Several are often responsible for serious diseases in plants, found in wet soil, freshwater, and polluted water.  Problems are most likely to occur in areas of poorly drained soil or that are over irrigated.  Although, pythium damage can occur anywhere after extended rainfall and at any time of the year.

If the plant still has some healthy white roots that are firm, it MIGHT be possible to save the plant.

Clean the roots by washing and rinsing under running water.  Cut all the damaged roots and cut a small amount of the healthy root as well. Wash the prepared root and replant it in free-draining soil.

Wash all utensils used in a strong bleach solution to sterilize. 



Photo by Howard F. Schwartz // CC by 3.0


Rhizoctonia is one of the fungi responsible for brown patches in lawns and damping-off of seedlings, crown rot of sugar beet, and more.

Root rot caused by Rhizoctonia causes a sudden, permanent wilting and complete collapse of leaves and petioles.  When studied, the root symptoms have dark circular to oval lesions that gradually form larger rotted areas on the root as the disease progresses.  If you cut into the root, the lesions are typically localized on the root’s external layers. 

When very advanced stages are reached, they will penetrate the interior area. Rhizoctonia can survive in any soil and is not restricted to poorly drained soils.  However, most severe in heavy, poorly drained soils or where pools of water occur.  The fungi will overwinter in the soil and plant matter, becoming active when soil temperatures warm up to 78o to 90oF.

The best treatments are to plant resistant varieties of vegetables and grasses and to improve drainage.


Thielaviopsis basicola

Photo by University of Kentucky Plant Disease Diagnostic Lab


Also known as black root rot, it is caused by a fungal pathogen Thielaviopsis basicola. It is characterized by dark brown or blacked spores within the root that is then followed by black lesions on the root.

Symptoms are characterized by plants wilting as though too dry, even though the ground is damp or wet.  When viewed in a bed of plants, those with black root rot appear stunted and give the appearance of needing fertilizer.  They often take on purpling and resemble plants with phosphorus deficiency.

If you see this problem, it is always wise to look at the roots to see if there are any brown or black rotted areas. 

Thielaviopsis root rot is something that can occur in more than 150 species of greenhouse and perennial crops. 

These plants include:

Astilbe, begonia, calla lilies, calibrachoa, cyclamen, fuchsia, gaillardia, geranium, gerbera, kalanchoe, lupine, pansy, penstemon, peony, petunia, phlox, poinsettia, primula, snapdragon, strawberry, sweet pea, tobacco, tomato, verbena, vinca, and viola. (list from Promix, accessed 01.11.2020).

It is a difficult problem to control and eradicate once it has started.  Very moist to wet soil, especially in a greenhouse from overwatering, creates the ideal conditions for Thielaviopsis.  Greenhouse conditions of high humidity and a lack of airflow exacerbate the suitable conditions for it to thrive.  It is an opportunistic pathogen and attacks plants that are under stress.

When we maintain the soil or substrate is continuously wet, with humid conditions, especially when accompanied by low light, this causes the plants stress.  Other contributory factors are over-fertilizing or doing so at insufficient levels, fungal attacks, insect infestations, rough handling of crops.

The sensible option is to discard the infected plants.  Crop loss from Thielaviopsis can be quite extensive if not controlled.  The good news is that by amending your management, you can prevent reoccurrence.

To prevent a reoccurrence, do not use the same containers. Thoroughly clean all equipment, shelves, greenhouse glass – everything.

Use good draining growing substrate; consider adding some grit. For future crops, avoid overwatering, avoid overcrowding and increase airflow.  Take care to fertilize correctly and reduce stress by controlling insects and handling plants carefully.

Whichever type; root rot is a serious problem.  Suppose an ailing plant is particularly precious to you.  You may consider it worth trying to save in the early stages.  You could try following the steps advised above for pythium and then replant into a container with a well-draining substrate.  However, in most instances, the only solution is to destroy the plant and start again. 


Related Questions

Do earthworms eat plant roots? No, earthworms mainly feed on dead plant tissue, microorganisms like bacteria/fungi, and mineral soil fractions. These Soil-Critters help to fertilize and guard your plant’s roots from diseases. Plants and worms live in a symbiotic relationship

How to tell if plant roots are dead? Carefully expose the roots of your plant. Healthy roots are usually white, firm, and scent-free. Roots damaged from excess water or root rot turn brown, mushy, and smell rotten. On the contrary, dehydrated roots turn brittle and a lighter brown shade.