“Leaf” It in the Garden

“Leaf” It in the Garden

Using leaves and leaf mulch in your garden

By Virginia Stephenson, Master Gardener
PHOTO: V. Stephenson. Leaf mulch as a natural uniform ground cover.

Traditionally, when fall rolls around we grab up our rakes and leaf bags, gather up all of our leaves, and dispose of them. But if you have a look at nature, where resources tend not to be wasted, you will see all the leaves lying in a carpet on the forest floor. This carpet of leaves protects young and tender plants during winter, provides food and shelter to small creatures, and eventually returns nutrients to the soil as the leaves decompose. Leaves and leaf mulch can do all these things in your garden, and more.

What is leaf mulch?

Leaf mulch is nothing more than leaves chopped up and possibly mixed with some grass clippings or other plant material. The easiest way to produce leaf mulch is with your lawn mower. Instead of raking up your leaves, collect them with your lawn mower, bagging them as you go, and, presto, you have leaf mulch.

Why mulch your leaves instead of leaving them whole as they are in the forest?

When you mulch your leaves, they become much denser and take up less space if you are storing them for later use. Mulch is easier to handle and spread in the garden and provides a more compact and uniform cover than whole leaves. As the leaves are already cut into small pieces, they decompose more quickly, returning their nutrients to the soil sooner than they would if they were whole.

When would I use whole leaves and when would I use leaf mulch?

If and when you mulch your leaves will depend on when and for what purpose you are using them.

If you are covering your garden perennials with leaves for protection in winter, you may wish to use whole leaves, as they will provide a looser cover, which will allow air to circulate, and make it easier for the plants to push through in spring. If you have access to oak leaves, they are excellent for this purpose, as they are quite fibrous and do not break down easily. They are therefore less likely to become a sodden mass weighing down your plants, making it difficult for them to emerge. When I have covered my perennials with leaves in the fall, I will often go out in the spring when it is getting warmer and the plants are ready to emerge and pull the leaf cover off the plants, so that the heat and light of the sun can reach them. I will, however, leave a wall of leaves around them, and possibly a few dry oak leaves partially covering them, to protect the emerging plants from any late frost.

If you wish to use your leaves as an organic fertilizer and benefit from their nutrients, then mulch them in the fall and spread them over your garden beds. In vegetable gardens or annual flower beds, they can then be gently incorporated into the top few centimetres of soil when you prepare it for planting in the spring. You can also pull back the mulch to create seed rows or openings for seedlings and leave the mulch on the surface of the surrounding soil. In perennial beds or shrub borders, spread the mulch around the plants and simply leave it there to decompose.

If you are interested in providing food and shelter for the small creatures in your garden, then use whole leaves to create a loose layer of leaf litter in your garden beds. Birds, small mammals, amphibians, and insects will all enjoy and benefit from this leaf litter.

PHOTO: V. Stephenson. Leaf mulch in foundation beds.

In my garden, I use both whole leaves and leaf mulch. In the fall, I gather the whole leaves from my lawn and spread them over my flower beds for winter protection. In the spring, when the garden is emerging (perennials), or ready to be planted (annuals), I remove the layer of leaf litter and run it through the lawn mower to create leaf mulch. The leaf mulch is then returned to the garden to cover the soil around the plants.

Note that the mulch should not be touching nor piled against the plant stems, as this may keep them too moist and cause them to mildew or rot.

What are the benefits of using leaf mulch in my garden?

Using leaf mulch to cover the soil around the plants in your garden beds has a variety of benefits both practical and aesthetic.

PHOTO: V. Stephenson. Leaves at the base of clematis to keep the roots cool.

Soil moisture: Leaf mulch will help to retain moisture in the soil. By protecting the surface of the soil from direct sunlight and exposure to hot dry air, you can reduce moisture loss from evaporation, keeping more moisture in the soil for longer periods. This retention of moisture can provide a variety of benefits to you as a gardener:

  • By retaining moisture, the mulch helps ensure that more of the water that you put in your garden goes into your plants. As a result, you may find that you need to water less often and can save money on water over the course of the summer.
  • We all know that the soil in containers tends to dry out very quickly and needs constant watering. Lyndon Penner, the head gardener at Riding Mountain National Park, is a big fan of mulch, and recommends using it in all your containers. A good layer of leaf mulch on the soil in your containers can help to keep the soil cooler and moister than if it was bare soil.
  • Some plants, like clematis, need to have their roots in cool soil and others, like astilbe, do best in moist soil. A layer of leaf mulch around these plants can provide these conditions and help them thrive.
  • The soil under the mulch stays soft and moist, which makes it much easier to dig and plant in than bare soil which has dried out and hardened.
  • Our clay-based soils are very prone to surface drying and cracking. The mulch layer covering the soil surface and protecting it from drying can help to prevent soil cracking.
  • Our clay soils, as they dry, are also prone to shrinkage with the result that in hot, dry weather the soil may pull away from your foundations. A thick layer of mulch in any garden bed against your foundations can help to keep the moisture in the soil and help prevent the deep drying which results in the soil pulling away from the foundations. Note that you do have to put the moisture in to start with and you should water your foundations in hot dry weather.

Weeds: Mulch will help to keep the weeds down by preventing weed seeds from touching the soil and germinating, and by keeping weed sprouts covered so they don’t get sun.

Fertilizer: Leaf mulch is an organic fertilizer, which will return nutrients to the soil. It is free, readily available, and easy to use.

Backsplash: A layer of leaf mulch on the soil around your plants can prevent mud from splashing up onto your plants during watering. This is a plus in terms of aesthetics and can also help to prevent the plants from being infected by soil-born fungi.

Aesthetics: Aside from preventing unsightly cracked soil, a layer of leaf mulch can provide a uniform and finished but natural look to your garden. It does not draw attention away from your plants to itself as some commercial mulch may. Empty areas between plants also look more natural and do not look as empty as bare soil tends to.

Are there cautions or counter indications for using leaf mulch?

Dust: Working with leaf mulch can be quite dusty, so you might want to wear a mask when bagging or spreading it, especially if you have respiratory issues.

Soggy leaves: Tree leaves are the best source for leaf mulch. Avoid using plant leaves which break down and become soggy after being frozen, as these can weigh down your plants or may cause them to rot.

Diseased or infested leaves: If your leaf source is diseased or infested with fungus or insects, avoid using these leaves to make leaf mulch, as you do not want to infect other areas or plants in your garden.

Grass clippings: If you gather and mulch your leaves using a lawn mower you are likely to have some grass clippings mixed in your mulch. This is not a problem if you let the grass clippings dry before bagging the mulch, as you do not want them composting in the bag. Avoid adding extra grass clippings, as too much grass can form a solid mat on your soil surface which can repel water and make it hard to get the water into the soil.

Wet soil conditions: If your soil is very wet in the spring, you may want to let it dry out somewhat before applying your mulch. The point of the mulch is to keep the moisture in the soil, but there is such a thing as too much moisture, which can be harmful to plants.

No leaves: If you do not have trees and leaves of your own, ask a friend or neighbour, who will probably happily donate as many leaves as you want from their spring or fall cleanup.

So, give it a go. Don’t throw away your leaves and see what leaves and leaf mulch can do for your gardening efforts.

FEATURED PHOTO: V. Stephenson.