Question
Hi,
I red your write about regarding cedar.  We are about to mulch around our trees. We live in NC.  Is there a certain mulch that you would recommend?  What are your thoughts on pine straw?  Thank you!  Jennifer

Answer
Cedar gets all the votes among those who want a waterproof mulch that does not retain water.  Cedar Chips and Cedar Oil repel many insect pests.  Cedar Chips discourage Chinchbugs, Pillbugs, Ants, Fleas and Termites.

Note that in reality, Cedar by any other name could be Juniper, Eastern Red Cedar, Juniperus virginiana.  Or it could be Thuja, Arborvitae, Western Red Cedar, Northern White Cedar.  Neither of these is REAL Cedrus.

Cedar and Pine chips have a dark side called 'Terpenes' -- especially Cedar.  Cedar owes its durability almost entirely to those toxic Terpenes.

But Chemist Bert Wilson, Owner of Native plants specialists Las Pilitas Nursery, in California, reasons that as a Climax plant, Cedar should at least in theory be the perfect mulch material: 'The climax Tree in a forest usually works for most plants in that forest...If you're using a Cedar from an East Coast forest, East Coast forest
plants that are not pioneers should be fine.'

Wilson's logic supports the position of Dr Linda Chalker-Scott, Washington State University horticulturist.  She says it's mere Suburban Myth that 'Wood chips made from Cedars kill landscape plants'.  Instead, says Dr Chalker-Scott, 'There is virtually no documented evidence for allelopathic activity in either Thuja or Cedrus species... Cedar, especially Thuja species, have developed chemical weapons against a number of pests and pathogens.  Researchers have found that Thuja plicata heartwood contains Thujaplicin, a water-soluble Tropolone' that inhibits growth of some Bacteria and Fungi.  'This antimicrobial activity is probably responsible for the rot-resistant nature of Cedar Wood.  There is, however, no evidence that this substance harms plant tissues.'  You can read her study here:

www.puyallup.wsu.edu/~Linda%20Chalker-Scott/Horticultural%20Myths_files/Myths/Allelopathic%20wood%20chips.pdf

There is a potential downside in non-Cedar Wood mulches, covered by the pro's in a joint Iowa/Kentucky State/USDA essay about Wood Mulch, 'Using Mulches in Managed Landscapes':

www.extension.iastate.edu/Publications/SUL12.pdf

They point out, 'Mulch derived from the bark of mature softwood trees, including Pine and Cypress, is very resistant to decay.  Bark from young softwood Trees decomposes more quickly because it does not contain the high levels of Lignin, Waxes and Tannins characteristic of bark from mature Trees.  Hardwood bark, because of its high cellulose content, also decomposes rapidly.'  (By 'rapidly', by the way, the authors do not mean days, or weeks, but seasons -- as in years of seasons.)

The Iowa experts make another point in the same Mulch essay: 'Organic mulches can dramatically impact soil microbial activity and nutrient availability.  Mulches with a high Carbon-to-Nitrogen (C:N) ratio, such as hardwood bark, ground wood pallets, straw and sawdust, can induce Nitrogen deficiency in plants by stimulating microbial growth, which depletes underlying Soils of available Nitrogen.'  THAT you DO NOT need.

Verdict: Cedar Mulch -- REAL Cedrus -- would be preferred.

Although I don't use it, Rosarians at the American Rose Society endorse Pine Straw with gusto: 'Pine straw is the mulch of preference at the American Rose Society's Headquarters (the fact that it is located on 118 acres of Pine forest may have something to do with this). Pine straw doesn't pack easily, is slow to decay, allows water and air to move through it, and can usually be acquired for FREE!'

You can read about the Rose Beds Mulching at the American Rose Society website:

www.rosesocieties.com/memphisrosesociety/Mulch.html

Thanks for writing.

THE LONG ISLAND GARDENER