Mulching Masterclass: How and When to Mulch Your Garden

Mulching your landscape beds and around trees and shrubs has many benefits if done correctly.  If applied incorrectly, mulch can kill a plant.  For me, the pros of mulching vastly outweigh the cons.

What is Mulch?

Mulch is any product spread on the ground to modify the environment around a plant.  There are a variety of mulches used depending on the purpose of the plants that are growing there.  Mulch for a vegetable garden may be different from mulch for a tree in the same landscape.

Effects of Mulch

Properly applied, mulch does many things.  It helps regulate soil temperature, especially in the spring and fall when the morning temperatures can be quite low and the afternoon temperatures quite hot.  Most mulches absorb rain and irrigation then gradually release the moisture to the plants.  A layer of mulch keeps weeds from growing by starving the embryo plant before it reaches the surface.  As mulch decomposes, it adds organic matter to the soil.  Mulch in vegetable gardens keeps fruits and vegetables off the soil, preventing problems caused by soil borne diseases.  Finally, mulch around the base of trees and shrubs protects plants from damage caused by mowers and string trimmers.

When mulch is improperly applied, it can hold moisture against the bark of a tree or shrub and cause rot, which eventually kills the tree.  Some mulches form a crust that repels water if they are not raked occasionally.  Some types of mulch can alter the soil pH if used for years.  Most organic mulches have to be topped off one or two times a year to replace the mulch that decomposes.  Some mulches, such as rubber or pebbles, can be difficult to remove if you change your mind.

Common Mulches

I cannot list all possible types of mulch because there are too many.  However, this is a fairly comprehensive list of mulches that are common and readily available.

Shredded Hardwood Bark

Shredded hardwood bark is a product of the timber industry as well as tree trimming companies.  The chunks are either shredded once for a coarse mulch or twice for a much finer mulch.  Both types will hold down soil and help prevent weeds from growing.  If you are sowing seeds, you will need to remove the mulch until the plants are about four inches tall.  Hardwood mulch is heavy enough it rarely floats during a rain or irrigation.

Shredded Pine Bark

Shredded pine bark is also a waste product of the timber industry.  If used for several years, pine bark can make the soil it covers more acidic.  Shredded pine bark is available in finely ground particles and in chunks called nuggets.  The nuggets are apt to float away during a storm.

Pine Straw

Pine straw is gathered by the timber industry from pine plantations.  It can also acidify the soil if used for several years.  Pine straw does not compact and lets air and water through it.  The straw from loblolly pines is often used as mulch.

Grass Clippings

Grass clippings can be a very economical mulch.  Let them dry for 2-3 days and then use them.  Grass clippings can mat and repel water, especially on slopes.

Leaves

Leaves need to be run over by the lawn mower once or twice before being used as mulch.  Whole leaves tend to float away while shredded leaves tend to stay where they are applied.  If you do not have enough leaves, you can usually get them free from your neighbors.

Sawdust

Sawdust from lumber mills is used as a mulch in some parts of the country.  Sawdust compacts and sheds water, so is not the best mulch for most applications.

Clover and Alfalfa Hay

Clover and alfalfa hay add nitrogen to the soil as they decompose.  The hay is often full of weed seeds.  Depending on where you live it can be very expensive.

Grass Hay

Grass hay is available in most places.  It decomposes quickly, so is best used for vegetable gardens where the plants will be harvested before the hay rots.

Paper

Paper can be used in two ways.  Shredded paper can be used as a mulch.  It decomposes quickly but if you have lots of paper shreds available, that may not be a problem.  Recycled paper in large sheets can be used in place of black or clear plastic.  Roll it out on your planting area and cut holes in it where you transplant things in it.

Cocoa Hulls

Cocoa hulls are a byproduct of the chocolate industry.  They are light and easy to handle.  Generally, they only last one season, so would work well in a vegetable garden.  Cocoa hulls are poisonous to dogs so do not use if you have a dog.

Pebbles, stone chips, gravel

These mulches do not decompose but do get carried away in shoe treads.  Because these materials last so long, they may be a problem if you need to plant something where they are spread.  Pebbles, stone chips, and gravel do better as fill for paths than as mulch in a garden.

Black Plastic

Black plastic is used by commercial farms.  It is spread over the planting area and weighed down with rocks or soil on the edges.  A slit is cut in the plastic where a plant is transplanted.  Black plastic warms the soil and conserves moisture and nutrients.  It has to be replaced after each crop.

Clear Plastic

Clear plastic is not used much anymore.  Weeds can grow under it because the sunlight can penetrate the plastic.  Clear plastic can be used to warm the soil if it is covered by another mulch latter to block the sunlight.

Landscape Cloth

Landscape cloth is a woven material that is used to block weeds.  It is easily penetrated by air and water.  Sometimes weeds grow in the small openings in the weave.  Covering the landscape cloth with another material can make it more effective.

How to Choose a Mulch

The choice of a mulch will largely depend on what is available in your area and what you are growing there.  If you have acid-loving plants, pine bark or pine straw works well.  In my area, we have grass hay but not usually alfalfa.  If you are mulching ornamental plants, you can use something more permanent like hardwood mulch instead of something that decays rapidly.  If you are growing vegetables, hay or straw will last a bit longer than the growing season in most places.  Plastic is not used by most hobby gardeners because it is expensive and difficult to spread.

How to Apply Mulch

Organic mulches should be applied to a depth of three inches.  Do not let the mulch touch the plants you are mulching.  Leave an area free of mulch that is about an inch around stems and three inches around bark.  Spread the mulch out to the dripline of trees and shrubs.  You will have to extend the area covered by mulch as the tree grows.  Large trees like white oaks or pin oaks can need a lot of mulch.

Organic mulch can increase the activity of microbes in the soil.  These microbes may tie up the nitrogen in the soil.  It is a good idea to spread some slow-release nitrogen under the mulch to keep your plants from running short.

Plastic and landscaping cloth is rolled out on the bed.  Be sure you anchor it well because it will beat plants to death in a storm if not secured.  Cut a slit to reach the soil and plant one plant in each slit.

Maintaining Mulch

With organic mulches, add a top layer of one inch a year each spring as plants begin to grow.  Occasionally rake mulch to break up any crust that has formed.

Need Recommendations?

Garden Plants Nursery staff are gardeners and can recommend a good mulch for any area in your landscape.  Give us a call at 931.692.7325 today.