When researching about the perfect soil to use for your plants you might come across the term ‘soil water retention’. If you’re asking yourself, “what is water retention in the soil” you’ve come to the right place.
Water retention in soil refers to the soil’s ability to hold on to water. When water falls on the soil, gravity pushes it down through the dirt’s pores.
In containers with drainage holes, you see this as the water flows out from the bottom. Outside, water is filtered through the soil and ends up in underground streams and aquifers.
Regardless of whether you’re growing in the ground or containers, improving your soil water retention will help you to water less often. Along the way, you’ll find yourself with healthier soil (and healthier plants) as well!
Soil water retention might seem like a complex and technical topic best saved for experienced gardeners or dedicated farmers. Don’t be intimidated though. The information in this article will help you understand what influences soil water retention and how to improve it with a few simple steps.
What is water retention in soil
Soil water retention relates to the soil’s ability to hold water. When it rains or when we water our plants, gravity pushes the water down through the soil. The rate at which the water flows can happen very quickly, very slowly, or not at all depending on the soil type.
We can measure water retention in soil in two ways. The rate at which the water travels through the soil and how much water the soil can hold.
The soil’s potential to retain water depends primarily on two factors: the soil type and the amount of organic content in the soil. Soil type affects the rate at which the water travels while organic content is what absorbs and holds the water.
Think of it this way – soil type, the amount of organic content in the soil, and the soil’s ability to retain water are all interconnected. Each one affects reinforces the next.
Why would I want my soil to retain more water
Building healthy soil should be the main goal of any gardener and healthy soil coincidentally holds more water. So increasing soil water retention is in the best interest of any gardener.
Healthy soil retains water very well, so in the pursuit of better soil water retention, you might actually end up with a healthier garden. Soil water retention is important because plants and other soil-born life need that stored water to survive.
As gardeners, we want our soil to retain more water. Higher soil water retention means that you don’t have to water so often, and the soil can withstand longer periods of drought. If you water your garden from a hose, increasing the soil’s water retention capacity is one way to reduce your water bill.
Watering less frequently can also mean that nutrients aren’t lost so quickly. Excess rainfall or overwatering flushes essential nutrients from the soil through runoff. Runoff depletes the plant’s food and can also cause water pollution when those nutrients end up in rivers and streams.
Long periods of drought can cause permanent damage to soils by degrading the organic content, causing crust on the surface, and deteriorate the soil structure through compaction. Increasing soil water retention makes the soil more drought resistant, preventing this harmful chain of events.
Soil water retention can also affect seed germination rates. If the soil dries out too quickly and there is not enough moisture between rains or watering, seeds will not be able to germinate. Seeds that are sensitive to temperature can also suffer since dry soils fluctuate temperature more easily than wet soils.
Increasing water retention in the soil directly impacts the amount of work you’ll have to do in the garden. Indirectly, it helps support healthy soil functions which will then support thriving and resilient plant life.
How to improve water retention in soil
One of the cornerstones of organic agriculture is building up the soil’s organic matter. Because of this, you can borrow some strategies from organic farmers to increase your soil’s water retention.
There are several methods you can use to improve water retention in the soil. Increasing organic matter is the most important. Tilling less frequently (or not at all) also helps improve soil water retention.
To build and preserve the amount of organic content in your soil, reduce tilling to a minimum, and keep your soil covered. If you’re feeling like a mad scientist, try inoculating your soil with mushroom spores for even more water retention.
Increasing organic matter
If you take anything away from this article, it should be to increase the amount of organic matter in your soil. Organic matter, also called humus (not to be confused with hummus), can retain up to 20 times its weight in water.
This impressive quality of organic matter means that you can dramatically increase your soil’s water retention by amending it with compost. Additionally, it will add to the overall health of your soil by making nutrients more available and feeding the microbial life.
In sandy soils, organic matter will help fill the large pores through which the water can easily flow down. In clay soils, humus will loosen up the particles allowing for excess water to drain down. Compost also reduces crusting on the top of the soil this will cause the water to disperse on the top instead of being absorbed.
Not all compost is created equal and will have the same amount of organic matter. Varying levels of nitrogen and carbon ratio will affect the organic matter’s water holding capacity.
Either way, introducing good quality compost is the best thing you can do to improve water retention in the soil. Increase the amount of organic matter in your soil by buying aged manure or try creating your own compost.
Once you’ve introduced the compost, preserve the organic matter in your soil by adopting gardening best practices such as reducing tilling and not leaving your soil exposed.
Tilling less frequently
Tilling is an agricultural practice where the soil layers are turned over. The idea is that it kills weeds and breaks up the soil, making it easier to plant. Rototillers are machines that till the soil. They can be hand-operated or used on a tractor and make the difficult task of getting the soil ready to plant much easier.
In recent years, mounting evidence has found that intense tilling actually hurts the soil structure by breaking up the topsoil and inverting the soil layers. By doing so, the organic content is degraded much more quickly.
I like to think of tilling as being a ‘special occasion tool’. It is extremely useful for preparing a new piece of land or mixing amendments into the soil. But if over tilled, the soil isn’t able to regenerate causing permanent damage to its ability to store water
Instead of tilling, try using no-till methods such as a broadfork to loosen up the soil and mix in compost. To deal with the weeds that tilling would have killed, keep your soil covered so they can’t grow.
Keep your soil covered
Covering exposed soil reduces the amount of water evaporation and helps preserve the organic content. You’ll want to keep your soil covered between seasons when there is nothing planted to protect the topsoil.
Use landscape fabric or used cardboard to create a protective cover over the surface. Or plant a ‘green manure’ cover crop, such as clover or vetch. Between seasons they will form a living blanket over the soil. When you’re ready to plant, or before they go to seed, cut them down and incorporate them into the top layer of soil to become compost.
Once you’ve planted, provide a good layer of mulch around your plants to lock in moisture and reduce weed pressure. With time, mulch will breakdown and can be turned into your soil as organic matter. Wood chips, straw, natural fibers, cardboard, clay pebbles, and many other materials make great mulch.
Mushrooms for soil water retention
Think of mushrooms like a flower that is attached to an inconceivably large network of roots under the surface. These mushroom roots can span for kilometers and play an essential role in healthy ecosystems. They help decompose organic matter, make nutrients available to plants, and improve soil structure.
Not so much is known about mushroom’s ability to help soil store water, but initial tests show promise. Mushrooms contribute to healthy soil, and as we already know, healthy soil retains much more water.
One way that mycelium directly affects soil water retention is by physically binding the soil particles together. This slows the rate that water travels, making it easier to hold and store. The structure of mycelium colonies also supports the permeability of the soil, making it easier for water to penetrate the surface instead of dispersing horizontally.
Another way that mushrooms help with water retention in the soil comes from their ability to decompose materials. Their role as decomposers in ecosystems provides a lot of organic matter for the soil.
There are still a lot of mysteries about how mushroom colonies function in the soil. We can say with confidence, however, that mycelium helps build healthy soil and healthy soil is the best at holding water.
Benefits of improved soil water retention
The best way to improve soil water retention is to introduce compost. Coincidentally, compost contributes to healthy soil in general and more thriving plants. Besides water retention, compost fertilizes plants, improves soil structure, prevents erosion, and mitigates extreme temperatures.
Compost provides plants with essential nutrients. It also strengthens their immune systems by supporting microbial life.
Amending poor soils with compost is the best way to improve poor soils that are high in clay or sand. These soil types aren’t normally very fertile so increasing the organic content in them improves the soil structure, helps feed that plants, and increases soil water retention.
Soil with good water retention properties absorbs the water instead of dispersing it. This reduces the risks of floods and makes crops more tolerant to drought. We can reduce big issues like stormwater management and crop loss by improving soil water retention.
Additionally, water has a much better heat-retention capacity than soil. So soils with a high moisture content don’t fluctuate in temperature so easily. It means that soils warmed through the heat of the sun take longer to heat, but are then much less sensitive to dropping temperatures at night.
The ability to moderate fluctuating temperatures helps with seed germination and can help plants survive in abnormal temperatures caused by climate change.
By improving the soil in general, pursuing better soil water retention creates huge benefits for the plants, soil structure, and hydraulic cycles.
Soil types affected by poor soil water retention
Sandy soils are most often characterized by their inability to hold water very well. The large particles of sand leave big spaces between them through which water easily flows.
This quality makes it very difficult for sandy soils to retain water and is the reason sandy soils are best for cactus potting mixes. For most plants, however, sandy soils become much too dry, too quickly. Without organic content in the soil to hold the water, it continues down into the earth.
Soil types with good water retention
The best soil for water retention is loamy soil with a lot of compost. Loamy soil has a combination of sand, clay, and silt which make up a soil structure that allows for water to drain out slowly. Loamy soil with a good amount of organic content will be able to hold on to the most water.
Clay soils retain water the best, but usually too well. The extremely fine silt particles that make up sandy soils make it difficult for water to go through. Instead of penetrating into the ground, soil that has too much clay will cause the water to pool on top and disperse horizontally.
Improving water retention in the soil is one of the best things you can do as a gardener. Lucky for you, it’s actually quite simple.
This means less time spent watering and a lower water bill. And in your garden, it means higher drought resistance, healthier soils, improved soil structure, and a stronger ecosystem. For the world, it means drought resilience and flood prevention.
Enjoy the benefits of better water retention by raising the amount of organic matter in the soil. Preserve the organic content by reducing tilling and keeping the soil covered. Then enjoy as you watch your garden grow more lush as you work less.