Cedar mulch – Friend or Foe?

There has been discussion of the use of Cedar mulch and can it be dangerous to the plants?  Really that depends on many variables but lets look at some of the known issues, the process it inhibits and some alternatives.

Sensitivity -Some people may be sensitive to the cedar fragrance, and they may find that it exacerbates allergy symptoms through either contact or smell.

Decomposition - Cedar will draw away nitrogen from the soil.  Typically only a problem when mulch is tilled into the soil.  Some argue this is a myth but for any of us who have used cedar extensively can attest that shredded cedar mulch decomposes quickly and requires it to be removed each year for fresh much.  An option is add it to a compost pile the year prior and let it begin to decay and if your compost is ready add it to the soil your planting in.  Make sure to take a pH reading of the compost before using it and compare it to the soil your planting in.

Acidic soil types - Cedar and pine mulches can add acid to the soil.  If you already have a low pH level cedar mulch can cause a problem.  You may want to add wood ash or lime to the soil if amending with cedar mulch.

Wet areas - low beds or wet spots can create an addition issue, but when adding mulch to it the problems grow significantly by promoting root rot.

Young plants - Cedar has been found to be toxic to young plants and seedlings.  Make sure if wanting to use cedar it is not in sawdust form or do not use on plants that have very shallow root systems such as celery or asparagus.

Beneficial bugs - The biggest benefit to cedar is it naturally repels insects.  But not just those pesky ones but also ladybugs and mantis, the ones we want around our plants.

So what is happening it the soil and the hubbub about Nitrogen.  We often use words inaccurately and using Nitrogen as it is, is one of those.  During natural decomposition you have organic material and to break down it needs oxygen, water and bacteria.  The oxygen and water start the process of decay, but decay is not enough.  Plants do not have mouths so they need to have their food is a water soluble form.

The decaying is a mixture of organic material, oxygen and water this process is called nitrification and creates Nitrites.  Once it reaches 72-78 degrees the bacteria move in and look for the Nitrites.  It is theses Nitrites the bacteria need to create Nitrates.  Nitrates are what the plant needs.

Back to the Cedar, this process takes longer, a lot longer and with natural inhibitors already in the wood it takes more for the process to take hold often directing the bacteria away from materials already needing to be converted and the essential oils in Cedar have been shown to kill these bacteria.  So now we need to amend the soil and we find ourselves in the catch 22.

So what can you do?  Cedar mulch is fine to use but on the balance of nature, sustainability and conservation you might want to avoid shredded cedar mulch except for trees, and hedges and perennial gardens based on items discussed if you want to use cedar in your vegetables choose cedar bark or chunk type mulches and be sure that no coloring has been added.  Many cedar mulches have a red dye added to give them a red appearance, cedar is actually an off orange, tan to brown color.

Remove the cedar before planting the next season and compost.  Replace with fresh mulch each year. Also water the ground heavily prior to placing mulch down.  After the mulch is down it will take up to 10x's more water to get it down to the roots of the plants.

Another option is to lay strips of ground fabric between plants, about 6" away from the base of the plants and place most of the mulch along those strips, keeping a thin layer near the plants.  Square foot planting will also reduce water consumption because the plant leaves will assist in keeping the soil at the right temperature and maintain water levels.  A good example would be zucchini.  A plant that requires to be planted in full sun but the leaves are often so large they shield the ground.  These large leaves serve multiple functions, photosynthesis and providing proper soil protection for the things the plant needs.  The sun is for the flowers, once set and pollinated it has done its job and now produces the fruit.  Mulch is not a huge help here.

If you are like me and love raised beds mulch may not be much of a help.  Often mulch will keep soil too wet and root rot will be a big problem.  My suggestion here is use leaves.  If you have a leaf shredder save a pile from the fall and use that as mulch.  It retains the same amount of water as the mulch, and it restricts weed growth.

No matter what you choose, keep in mind what you place in your gardens can always benefit or hinder your garden and each season needs to be addressed each year.  Meaning more rain less mulch or less rain more mulch, also keep an eye on where you get your mulch.  In recent years there have been reports of  lead in mulch coming from China and India as well as Canada, it is always a good idea to read the label or visit your local garden center, many of which sell locally produced mulch products and often cost far less than a per bag from a chain store, unless you only need to do a small area.  A cubic yard of mulch (about a ton) usually cost me about $35.

Happy gardening, farming and eating!