Organic Mulches

A Mulch for Every Purpose

Fortunately, organic gardeners have a wide-ranging choice of mulch materials, each contributing a special set of benefits:

Dry leaves. If your yard is heavily treed, lucky you; you have a free fall bonanza of mulch. All you have to do is shred the leaves with a lawnmower and you will have cubic yards of organic mulch. It’s best to shred them to keep them from blowing away or compacting. Shredding also aids the decomposition process. Oak leaves are especially wonderful for mulching acid-loving plants, as they will slightly acidify the soil over time. Take care not to include leaves from trees that have recently suffered from bacterial diseases like canker or anthracnose.

Bark. Bagged bark mulch can range from large nuggets to mini-nuggets to the shredded form. We don’t recommend the large nuggets because they repel water and prevent it (and any nutrients that come with it) from getting to your plants’ root system. This is also the bark form that is available in various colors. (We do not recommend tinted bark for organic beds because of the chemical dyes used in the manufacturing process.)
Pine, cedar or cypress mini-nuggets are excellent mulch, as is shredded bark — as long as it’s not tinted. Please note that pine bark is slightly acidic and will eventually alter the pH of your soil over time.

Straw. Not hay, which is full of seeds that will sprout in abundance. Make sure the straw is “aged” and very dry. Straw is best for winter mulch, as it won’t compact under heavy snow/ice, and is the mulch of choice for strawberry beds. It keeps the fruit from becoming muddy, allows for good air circulation and breaks down beautifully to add organic matter around the plants.

Pine straw. This is not really straw, it’s long, dry pine needles that have been baled to look like straw. Their pH is on the low side, which is ideal for mulching blueberry bushes, hydrangeas, azaleas, rhododendrons and camellias. It’s stable, breaks down evenly and is a wonderful soil conditioner for those not fortunate enough to have sandy loam.

Cocoa hulls. Who doesn’t want a garden that smells like chocolate? While the aroma may only last for a couple of weeks, the hulls break down quickly and the humus makes its way into the soil faster than other materials. The downsides are that because it decomposes fast, it becomes brittle/light and can blow around. It can also be hazardous to dogs if they eat it, so consider this carefully beforehand.

Wood chips. Sometimes local landscape and even municipalities will provide free wood chips to local residents to keep it out of the landfills. These are “fresh” wood chips and have the potential to burn plants, shrubs and even young trees if applied in this state. We only recommend you use this type of mulch for walkways or compost-making. If you can determine that the wood was chemically treated, do not use it in any instance.

Grass clippings. As long as the grass has not been treated with chemical herbicides or gone to seed, start with a relatively thin (1-2”) layer of dry grass clippings that will serve as a rudimentary mulch. Resist piling a thick mat of green clippings onto your garden beds — that will result in a foul-smelling mess of compacted slime. Be sure the clippings are dry before you add them to the previous mulch layer, and just add a couple of inches at a time. After the growing season is over, the clipping-mulch can be incorporated into the soil to further decompose over the winter months.

Newspaper. This can be a very effective natural weed barrier. We recommend using sheets of newspaper instead of plastic under more decorative mulch because it will naturally break down to feed the soil, and simultaneously allow water and nutrients through to the plant. Most all newspaper printers use organic black ink now, so there are no worries about chemical dyes — just don’t use color pages.

Animal manure. Not technically “mulch,” but can act as such if sufficiently decomposed, which is key. It is, of course, also a soil conditioner and fertilizer. Never use fresh manure as it can burn/damage young roots, and never use cat, dog or pig manure. It bears repeating that the manure needs to be fully composted before using.

“Living mulch”. As the name says, this is mulch that grows, as in a cover crop. Alfalfa, winter rye and buckwheat are good choices because they fix nitrogen in the soil, but you could also use a creeping ground cover like sedum, thyme or any other shallow-rooted plant which doesn’t sap a significant amount of water or nutrients away from the plants you’re growing.