How to Choose Mulch for your Garden

education program about wood chips

Mulching is a garden task that beautifies your gardens while making them easier to maintain. Mulch keeps weed seeds from sprouting and holds moisture in the soil to reduce the number of times you need to water. Generally a layer of mulch should be ~2” deep to be effective, but coarser materials can be as deep as 4”. Regardless of depth, mulch should never cover the crown of perennials or make contact with the trunk or stems of trees and shrubs. It is best to apply mulch before temperatures get too warm, in late April or early May.

If you ever shop for mulch at a big box store, you will notice the wide variety of options for mulch. Not only are there bark mulches, both shredded and chipped, but there is straw, leaf mold, compost, and rock. These materials all have their place in the garden.

Garden areas that are replanted every year with annual flowers and veggies do best with mulch that decomposes quickly, as it will have to be replaced every year. Composts, like leaf mold, can be used as long as it has been treated for weed seeds.  These also add nutrients back into the soil, which is often beneficial in intensively planted areas. Straw is another option for these areas, and bales are often very affordable.

Beds that are planted with trees, shrubs, and perennial plants can be mulched with materials that decompose at a slower rate, like shredded bark. Shredded bark is the most common kind of mulch, and there are plenty of options available. Bark mulch is often dyed to give it a more consistent appearance, with colors like brown, black, and red being most common. Other times, bark mulch is sold by species of tree, like pine bark mulch or cedar mulch. Pine bark mulch is very lightweight, which makes installation easier, but also means that it can wash out in heavy rain events. Cedar mulch is decomposes slower than most bark mulch, and is reported to repel harmful insects.

Stone mulches, like pea gravel or rock chips never decompose, but also don’t hold moisture in the soil or return nutrients to the soil. In sunny areas, stone can actually increase evaporation rate in the soil. This can be beneficial for plants that like dry soils, but damaging for many other plants. Stone mulch is a great option for walkways, as they still keep weeds down.

There are also products that should never be used as mulch, including sawdust and wood shavings. These products actually absorb nitrogen from the soil, depriving plants of the vital nutrient.

Prepared by Lindsey Smith, Collections Curator