What Is Root Rot?
At the most basic level, root rot is a plant disease, but the key is in learning what factors cause this disease. The disease can be caused by waterlogged soil or various kinds of fungi. Soil can become waterlogged for a number of reasons, including poor drainage, continuous heavy rainfall, and overwatering. Overwatering may be the most disconcerting of all. You know that your plants need water, and you feel that you are being conscientious by supplying them with that water. But this is a case of “too much of a good thing.” Even overwatering or an unusually rainy period, however, are often not enough, in themselves, to cause your soil to become waterlogged. Their great enabler is poor drainage. Water runs through a sandy type of soil like a sieve; it is rare for such a soil to become waterlogged. But a clayey soil holds water for a long time. So it is usually the combination of poor drainage and excessive moisture that makes the ground waterlogged. You may not think of plant roots as needing to breathe, but roots do need oxygen. That is why waterlogged soil is a problem for them: They drown in it, rot, die, and become useless to the vegetation they support, eventually resulting in the death of the plant if you fail to solve the problem. Ironically, roots rotting from sitting in too much water are unable to absorb water and transport it to the rest of the plant, which wilts. Sometimes, the cause of root rot is not as simple as waterlogged soil. The direct cause may be a fungus, such as Phytophthora. But, just as poor drainage enables excessive water to become a problem, so waterlogged soil is an enabler for Phytophthora. Fungi thrive under wet conditions; Phytophthora rarely becomes an issue in soil that drains well.
How to Identify Root Rot
The reason that root rot is so hard to detect in a timely manner is that it is developing underground, out of sight. Despite the name, “root rot,” gardeners usually spot signs of the disease in the plant’s leaves, not its roots. By then, unfortunately, the damage has already been done. Yellowing leaves can be a sign of root rot, and the leaves may drop off. The leaves may also become distorted (smaller than usual, twisted, etc.). Once you do inspect the roots, you may find that they are a different color than normal (darker, reddish-brown, etc.) and stink with rot. Yet another sign of root rot is that, no matter how much you water the plant, it always looks wilted.
How to Prevent or Treat Root Rot
Preventing root rot in the first place is a lot easier than dealing with it after you’ve got it. Providing your yard with good drainage and avoiding overwatering are the two best prevention tips. It is difficult to know how much water is too much, in terms of an actual measurement. The best way to determine if a plant is watered properly is to dig down into the soil just outside its root zone (close enough to see what is going on there but not so close that you damage the roots). Most plants prefer to have an evenly moist soil throughout their root zones. So if you find the soil dried out down there, then you are not watering enough. But if you find it soggy, then you are overwatering. A yard’s drainage can be improved in a number of ways, including by:
Mixing amendments into the soil, such as compost Installing French drains Growing your plants in raised beds
If you fail with prevention and end up with root rot, all may not be lost if the plant in question is small enough (for example, a perennial rather than a big tree or shrub) and if you have caught the problem in time. Houseplants, which are notorious for root rot, can often be saved because they are growing in containers, giving you easy access to their roots. You can treat minor cases of root rot by first digging up the plant, washing the roots, and removing (with a sterilized cutting tool) the diseased parts. In replanting it later, you can either return it to the same spot after improving the ground with compost or else transplant it to a better spot. Either way, giving your plants a friable soil to grow in may help you avoid the problem of root rot in the future.
Preventing Root Rot With Smart Plant Selection
Nor should you overlook the importance of smart plant selection. If you know you have a soil that stays wetter than is ideal for most plants, grow plants meant to be in or around water and/or plants that tolerate poor drainage. Examples include:
Northern blue flag (Iris versicolor) Willows, such as pussy willow (Salix discolor)
And avoid growing the plants that are most susceptible to root rot, including:
Mountain laurel (Kalmia latifolia) Rhododendron spp. Andromeda (Pieris japonica) Yews (Taxus spp.) Heather (Calluna) Mediterranean plants such as English lavender (Lavandula angustifolia)
