Mulch. A topic that doesn’t grab attention the way shining tomatoes or beautiful produce-laden trellises do. But, when it comes to finding success in the garden, mulch is one of the best tools in the organic gardener’s toolkit. Using mulch supports the health of the plants and soil organisms, reduces workload, conserves water, and improves the soil.
If you’re asking yourself if should you bother with mulch, the short answer is yes you should (if you can). The benefits listed above will create a more productive garden out of less work. In this article we’ll explain why mulch is so important and offer some tips to get you started.
So, why mulch?
1. Mulch Protects The Soil Surface
From what? From sun, water, wind and cold.
It might seem that soil is pretty tough, or that maybe you don’t live where the soil is subjected to extremes. But, a regular sunny summer day, even in a temperate climate, raises the temperature of the soil surface well past the ambient air temperature (more on temperature below). Dark, bare soil gets hot in the summer in much the same way as asphalt does. This in turn stresses the plants and the shallow soil life that the plants depend on.
And then there’s rain. While rain may seem harmless, a single intense downpour can wash away a fair amount of bare topsoil (depending on the specifics of your garden). Losing a little topsoil might not seem like a big deal, but you have a finite layer of it to work with. And a nice deep topsoil is much more supportive of plants than a thin one. If a large amount of it washes away in an intense thunderstorm, then the subsoil beneath it doesn’t just turn into topsoil by the next season. And replacing topsoil, (unless you purchase it) takes a VERY long time, like, years/decades/centuries.
Lastly, the sun, wind and water might just work together to form a crust on the surface of unmulched soil. Some soil types are more prone to this than others, but a crust formed on your soil reduces air and water infiltration, which will stress your plants. As I’ve heard it said, if you don’t mulch your soil, the top of your soil will become the mulch (and no longer part of the functioning soil).
But you don’t have to take my word for it. One of the tenets of soil health, according to the pioneering and famed regenerative farmer from North Dakota, Gabe Brown, is that your soil must be covered. As he puts it, soil needs “armor on the surface” at all times, and he points out that nowhere in nature do you find soil left barren. At least not for long before weeds fill in and do their job.
2. Helps Keeps Plant Temperatures Steady
What do we mean by this? Mulch is like a handy blanket for the soil, one that helps keep it both cool AND warm as needed. As mentioned, an unmulched soil surface can get VERY hot during a day with full sun. Well over 100°F (38°C). This raises the temperature of both plant roots and the ambient temperatures surrounding the plants. In contrast, the shade provided by mulch keeps the soil, plants, plant roots, and soil life much cooler.
Why does this matter? Because every plant has a range of temperatures within which it photosynthesizes and respires optimally. Temperatures that are higher than the plant prefers reduce photosynthesis and, therefore, reduce plant growth. The size of the ambient temperature change that occurs between day and night also affects the plant. Mulching helps to reduce drastic daily temperature swings between extreme heat and cold.
Lastly, a nice layer of mulch also insulate’s a plants roots from cold. For many grower’s this is something we’re more concerned about when it comes to overwintering certain perennials. But mulch, along with plant coverings, is also useful to protect annuals from unseasonable frosts. If you have a plant that is just barely hardy in your zone, it definitely would benefit from big blanket of mulch to keep it insulated during the winter months.
3. Mulching Retains Water
A nice layer of mulch keeps rain and irrigation water from evaporating. It’s that simple. Yes, we want to conserve water while making sure our plants have enough to drink. But we also want to avoid subjecting our plants to cycles of intense, rapid drying followed by overwatering. Applying mulch to the surface keeps water levels more stable and avoids these extremes.
While most plants should have the opportunity to dry out a bit before watering (we don’t want them soggy all the time), you don’t want them to dry out rapidly and frequently. As an example, blossom-end-rot is a common problem with tomatoes and other nightshades related to watering. Blossom-end-rot is a literal rotting of on the blossom end (the bottom end where the blossom was, opposite from the stem) of the vegetable.
A calcium deficiency is directly to blame, but the calcium deficiency itself is often caused by under and overwatering. This watering problem then affects the plant’s ability to use calcium. Mulching maintains a more steady supply of water to the plant which can help prevent blossom-end-rot and other water-stress related problems.
4. Organic Mulches Feed the Soil Food Web
Have you ever pulled back a pile of organic debris (like old grass cuttings or leaves), and found bugs and other critters scattering? Those critters are feeding on the debris, sheltering in it, and preying on the other creepy crawlies hiding in there. In my own garden, I often notice lots of earthworms right at the soil surface when I pull back a nice thick layer of mulch. This is fantastic news, because their burrows allow oxygen and water into the soil, among all the other magic that earthworms do.
But worms aren’t the only ones. There’s a whole soil food web comprised of countless insects and microorganisms such as bacteria, fungi, nematodes, and protozoa that benefit from the shelter and food provided my surface mulches. These organisms work together in a crucial ecosystem that supports and feeds your plants. See this video for a useful introduction to the soil food web. Generally, the more life in your soil the better.
Protecting the many residents of your soil is also a good reason to mulch thickly for the winter if you live in a cold climate. The mulch provides food and insulates the soil from the coldest temperatures.
One thing to be mindful of, however, is some mulches do support pests like slugs. So if you live in a climate where slugs and snails are a problem, you’ll want to select a mulch that doesn’t encourage them. Straw mulch, for example, is not recommended for locations with slug problems.
5. Reduces Weed Pressure
Preventing weeds is probably the most common reason gardeners use mulch. There are many ways to combat weeds, such as good old-fashioned weeding, avoiding tilling, and using flame weeders, tarps, etc. But one of the easiest ways to stay ahead of them from the start is to use mulch on a freshly planted bed. The time and effort spend on spreading mulch at the start of the season is regained when you don’t have to spend that time weeding.
Once a weed seed germinates near the soil surface, it needs sunlight to grow. Blocking sunlight with a layer of mulch is an easy way to prevent the growth of young weeds. The thickness of this layer might need to be anywhere between 2-4+ inches (5-10 cm), depending on how closely the material packs together and blocks light.
Summary and Tips
In short, mulching your vegetable garden has the following benefits:
- The topsoil is protected from erosion
- Temperatures are moderated from both hot and cold extremes.
- Moisture levels are more consistent with less rapid drying.
- Soil organisms are sheltered and fed.
- Weed pressure is reduced.
How To
So the next step it to track down some mulch and apply it. See our article on the many free or low-cost mulch options. Spread your mulch to a thickness where you think it will block light. Note that mulch should not directly touch plants if you can avoid it, so pull it away from existing plants slightly. If you need to direct sow seeds into your mulched bed, just pull the mulch back where needed and plant. When the plants have germinated and grown larger you can redistribute the mulch again.
Other Considerations
It’s worth noting that not all types of vegetables and gardening setups require mulch. For example, I would probably not mulch between my carrots, because I plant them densely, and once they germinate, their tops will crowd together. But i might try and spread some mulch in the slightly larger space between carrot rows. And I will mulch any large spaces between the last row of carrots and the next vegetable.
Some folks also plant densely or interplant in such a way that the plants themselves rapidly shade the soil and carry out many of the functions of mulch. And to even further complicate things, there are also “living mulches” to consider, which are basically smaller plants you grow on purpose beneath your main crop. More on that topic to come.
If you have any questions or thoughts about mulch to share please leave a comment! Thank you! Happy gardening,
