Mulching for Moisture Retention
Say it with me, gardeners: “Mulch is my life”. Well, maybe not, but mulch is one of the most important components of successful and resilient gardening, particularly in an arid area like Lethbridge. To be clear, mulch is any material that is spread around the base of plants to protect, insulate, or add nutrients to the soil. Let’s dig into it!
There are many different types of mulch and times to use them. Early spring is one of those times, as we head (hopefully) into our heavy June rains followed by high July temperatures: you should be thinking about ensuring your garden areas are mulched effectively. It’s a great time to put a little turf seed in, add extra lettuce seed to the garden, and make sure you mulch any new perennial installations or annual (vegetable/flower) beds and pots to protect the soil and roots from large amounts of rainfall and increasing heat. Beds should be watered well before mulching (after a rainfall is perfect) and the mulch should be dampened if it is dry to avoid removing moisture from the soil. In the summer, it’s a great practice to add mulch to annual beds and pots (vegetables and flowers) every time you weed. Similarly, fall is great time to heavily mulch trees/shrubs that have gone dormant to trap moisture in the soil and offer insulation through our frequent warm chinooks. Furthermore, mulch is a MUST for fall seeding – throw your seed and then throw a thin layer of mulch over it to protect the seed from wind and keep it in contact with the damp soil until it germinates.
Here are some common mulches and their uses:
WOOD MULCH
Simply, shredded/chopped/chunked wood and bark. It can come in all types, colours, sizes, shapes, and costs. In the end, all wood mulch functions the same way: it insulates an area against heat and cold (or movement between those two extremes), traps moisture in the soil, increases humidity in the microclimate (due to evaporation from the upper levels), slows weed growth, and adds aesthetic appeal (like the hem on a dress). Wood mulch should be used on bare soil areas under trees, in and around plants in perennial gardens, and thickly for pathways. Wood mulch is pure carbon, so as it breaks down it quickly binds with nutrient ions in the soil. For this reason, it shouldn’t be used in annual vegetable gardens (except for pathways that are kept separate from the growing areas with a border). Also, it should be raked back when amending perennial beds/shrubs/trees, then re-placed on TOP of the soil to avoid too much breakdown around plants. Wood mulch shouldn’t be dug into the soil. If you’d like to refresh your mulch for color, simply pile a thin layer on top of the old. Wood mulch, ideally, should be 3 inches through the growing season and up to 6-8 inches for the winter.
WOOD SHAVINGS/SAWDUST
Just another form of wood mulch, but softer and breaks down faster. These products have great uses in pathways and building new bedding areas, piled on removed sod, weeds, grass clippings, and dirt. It has a great function of keeping down the smell of decomposition, and bees LOVE IT for building the walls of their combs. Obviously, not great in the wind.
STRAW
Has great use in vegetable gardens to protect the soil from heavy rains and hot summer sun. Straw is inexpensive, lightweight, and light in colour (which helps reflect sun during the heat of the day). Straw will help trap moisture in the soil and insulate from temperature fluctuations (it can help protect seeds from frost in the spring and plant roots in the fall). It is very difficult to source seedless and/or organic straw (because organic farmers put their straw to use in their own operations), so the regular side-effect is wheat growing in your garden, which is what I like to call a “mulch crop” (offers high-nitrogen seedlings that are easy to pull and you just leave them on top of the soil). I use Simply Straw animal bedding, which has been cleaned of dust and can be purchased in bagged format at UFA.
GRASS CLIPPINGS/HAY
This high-nitrogen mulch is great for a vegetable garden, or as an under-mulch in your perennial garden, as it adds nutrients to the soil as it decomposes (rather than removing them). However, there is a risk of seeds in your garden beds, and grass and hay is quite difficult to remove. I like to use hay in areas where I am building the soil or a new garden bed (see wood shavings, above), and I only use grass clippings that have no seed. This is almost impossible if you live in an urban area, as Kentucky Bluegrass sends up seed heads almost as soon as it starts growing in spring.
COMPOST AND/OR SOIL
One of the ways I mulch is by dropping handfuls of damp soil into bare areas. This works in the vegetable garden (or any annual bed), in fruit plantings like strawberries, in your flower pots, and your turf areas. Soil acts as insulation, offers fresh areas for rhizome/root propagation, and adds nutrients. Note, if you have a carbon top-mulch (wood, straw, etc), make sure to scratch it back, mulch with soil, then replace the carbon mulch on top.
LEAVES
Piling your fallen leaves in gardens and shrub/tree wells (or just leaving it where it falls) should be part of your fall routine. Leaves offer insulation, insect overwintering habitat, and cost nothing. Our Lethbridge canopy (generally) doesn’t contain trees with leaves that are toxic to plants, so there is little worry that they will have a detrimental effect on your vegetable crops or soil. In fact, I use Manitoba Maple and Green Ash leaves piled on my fall-planted garlic/spinach beds and leave them in there to decompose as the plants grow through the summer. Before heavy rains in spring, it is best to thin the leaf layer to 3 inches (remove the bulk to a covered compost pile), as large volumes of dried- out leaves can be a fire hazard (but that’s another blog). Remove leaves from hardscaping (driveways, walkways, stairs), as they can be very slippery when wet make snow shovelling an impossible chore.
CARDBOARD/NEWSPAPER (“Sheet mulch”)
These organic sheet mulches are generally used under wood mulch for pathways or under loads of soil in raised beds. They can also be used under wood mulch in perennial/shrub beds to greatly reduce weed growth. The trouble with this use is that organic sheet mulch becomes almost impermeable when it is dry, so would cause water to run off the bed. Not a great use in Lethbridge unless you have an extremely damp area around, say, a willow tree.
INORGANIC MULCH (sometimes called “black mulch”)
Either landscape fabric or rock. I do not recommend rock as a mulch in Lethbridge, as it greatly increases soil temperatures and compacts our clay-based soils (leading to weed growth and lack of water absorption). Fabric, however, can be used on top of the soil to stop weed growth. Landscape fabric is often used in large vegetable gardens/farms, with the plants placed through holes at regular intervals in the fabric. This traps moisture within the soil and often growers will place soaker hoses under the fabric so that no additional irrigation water is lost to evaporation. Because of the colour (black) it often requires straw mulch placed on top before summer to stop critically high soil temperatures. Floating row cover is another fabric that can be used directly on the soil as a mulch to trap moisture and decrease soil temperature. It can be rolled back to amend and turn the soil and then replaced for the next year.
Finally, another purpose of mulch is to protect and enhance the soil structure that supports the plant life in your garden/yard. One of the most critical components of good soil is aeration, and one way to maintain good flow is to keep it light and fluffy. In clay-based soils, that means avoiding compaction. Piling mulch up and avoiding walking on garden beds will allow the soil to better absorb moisture and make weeding a breeze.
Say it with me: “Mulch is my life”.
