Mulch, Compost or Fertilizer?

The best fertilizer is the gardener's shadow.

~Author Unknown

A while back reader Christine asked me to write about compost. She wants to recycle waste from her kitchen and garden rather than send it to a landfill. Composting and mulching are great ways to make your waste work for you.

Mulch is material that is laid on top of the soil and left to decompose as a top layer. It can be leaves, wood chips, grass clippings etc, that decay and enrich the soil. Beauty bark is not recommended as it is said to contain salts, which can harm plants and soil organisms. Rocks and decorative stones are considered a more permanent form of mulch, and while they provide minerals as they break down they won’t necessarily enrich the soil like decaying plant material. Mulch helps to smother seeds that will be future weeds and keeps the soil moist and cool in the summer. It is a natural and easy way to nourish your soil as it releases nutrients gradually, just like nature does. Take a walk in the forest and you’ll see the soil covered with fallen leaves and plant debris, leaving a loamy rich top layer. In her book No Work Garden Book, Ruth Stout writes she only mulched, never weeded, never messed with compost and stopped fertilizing. She was quite successful by simply covering her soil with hay. Since mulch keeps your soil cool from the sun’s rays you may want to remove it from vegetable beds in spring so the sun can warm the soil for better seed germination before spring planting. All my fall leaves go straight onto the garden beds just as soon as they are raked, like a blanket, so they are mulch, not composted. You can find more information and photos of my leaf mulching in September’s post titled “Fall Cleanup, More or Less”.

Compost is the result of a pile of mixed plant debris (grass clippings, leaves, stems, twigs, vegetative food wastes) that has heated up and decomposed into a fine, dark, crumbly material and is also nutrient rich. It is not considered fertilizer by some experts but Organic Gardening magazine says it is. In fact OG maintains that if you use compost, mulch and cover crops you may not need to use any fertilizer.

Commercial composting facilities create compost that has heated up enough to kill weed seeds and disease pathogens. You can buy it in bulk or bags or you can create your own by simply corralling and layering ‘green’ materials and ‘brown’ materials. Green materials are grass clippings, weeds, green leaves/stems, coffee grounds. Brown materials are dried stems, twigs, dried leaves, shredded paper. Thinly layering each is the way to create your pile and once it heats up, turning it with a garden fork brings air into the process and helps it to break down. Come spring there will be lots of dried, dead brown plant materials to remove from your garden beds and green grass clippings (the first few cuttings) high in nitrogen are great to mix together for your compost pile.

I compost most of my chopped up plant trimmings, weeds, all of my organic vegetable kitchen waste, coffee grounds, tea leaves and egg shells (shells supply calcium to the soil). The finer the materials are chopped the quicker the breakdown. You can chop by hand or by running a mower over large leaves and stems or dumping the lot into a garbage can and plunging in a weed eater (string trimmer). The plant materials I exclude from my compost heap are large woody branches and rhododendron leaves, both of which take too long to decompose, also no trimmings that will contain seeds go in. My compost doesn’t get hot enough to kill seeds. If viable seeds remain in compost they will sprout and you’ll have to weed later. Nor do I include rose leaves (which often carry disease) and any leaf or plant material that appears or is known to have disease because home compost doesn’t often get hot enough to kill disease pathogens either. I live in the city where we have free recycling for yard waste. Any undesirable materials go in that bin, which is composted at a commercial level and does get hot enough to kill seeds and pathogens. 

Compost needs nitrogen to get it to heat up quickly. There are compost starters you can buy in a box but are expensive and I think more a gimmick than necessary. Early spring grass clippings are high in nitrogen and free if you have a lawn. Alfalfa meal is inexpensive and high in nitrogen if you don’t have grass. A few cups of that added to your pile will start the process and the balance of the bag is great fertilizer for your roses. (Be sure to lightly mix the alfalfa and any organic fertilizer you use into the soil surface so the microorganisms can break it down to release the nutrients.) A pile of plant trimmings with a good mix of green and brown materials will decompose and will smell earthy. The pile that just rots and is smelly has too much of one material.

There are 2 ways to make compost: aerobic and anaerobic.

Aerobic piles are turned about once or twice a week. Aerobic compost finishes faster, between 2-6 months given sufficient heat generation, water and volume. To get finished compost in 2 months the green/brown ratio is important and you turn it daily for the first week or so. Pile temperature should remain between 135 and 155 degrees for 3 days to kill seeds and most pathogens. If you don’t want to pay that much attention to it, it will simply take longer to break down. Mine usually takes more like 6 months. When I had a pile in four sided wire fencing, a hay fork was my tool of choice for turning the pile, with 5 skinny, long, curved prongs. A shovel or pitch fork can be used also but were awkward to me. You turn the hot core out and the cooler sides in creating a new pile each time, which gets more of the material to heat up. The more heat the quicker the decomposition. Moisture is important too. You need some but not too much. Most articles say as damp as a wrung out sponge. You can cover the pile in winter if you get a lot of rain, but in a dry summer you may need to hose it down now and again.

Anaerobic piles are never turned. You just keep adding materials in green and brown layers to the top. Finished compost is pulled out from the bottom of the pile. Plastic bins designed for this type of compost have a door at the base where you can shovel out finished compost. Anaerobic compost can take a year or so to finish the bottom layers.

Since winter keeps many of us out of our gardens, it is a good time to research compost bin designs, think about what kind of composting will work for you and where you might like to locate your pile. What ever style you choose it needs to allow a pile at least 3 feet tall by 3 feet wide. This size or bigger heats up best. The better the heat and aeration the quicker the decomposition and the sooner you can spread it on your garden. Some people simply make a pile with no boundaries. Some choose to corral their pile by making a ‘bin’. Some use found wooden shipping pallets, stood upright and fastened into a square, some use concrete blocks stacked to make a 3 sided bin and some use a big circle of chicken wire. There are many commercial designs made of plastic. One is even made to tumble by simply kicking it around, eliminating the need to mix it by hand. Some municipalities offer wire or plastic bins at a discount to encourage composting which cuts down on land fill usage. What ever you do, if you choose to turn your pile, make sure your bin will allow you to get in there easily and often with your hay fork. Having two aerobic piles side by side is helpful, because at some point you need to stop adding to a pile to let it decompose. All the while you keep finding plant material in your garden to add, so a second pile is needed.

The ‘bin’ I have now I made from a 55 gallon pickle barrel. To use less garden space I adapted a ‘spin’ design I found on the internet (sorry but the site is no longer up or I’d include it). I made it to hang between 2 fence posts so I can spin it on an iron bar that I inserted through the barrel and both fence posts. I live near the now vacated Nalley's pickle factory. When the company closed I bought four food grade barrels for five dollars each and used one as a composter and three for rain barrels. Finding food grade barrels was important to me as I garden organically and wanted to know that no chemicals were ever stored in the barrels I was going to use.

Worms help decompose plant debris too. Normally they will come up into your pile from the soil underneath, but since my bin is a ‘closed’ system I toss in worms as I find them. They must thrive in there as they have multiplied by the time my compost is finished and ready to spread. When your compost is finished you can either spread it as a top dressing on your soil or dig it in. Some say you must dig it in for it to improve soil structure but that’s a lot of work. I just leave it as a top dressing and let the worms and soil organisms mix it all up over time. It seems to work.

I hope this has been a helpful overview and perhaps an incentive for you consider composting in the near future. Happy composting Christine!!

In bloom in my garden today: Daphne caucasica ‘Summer Ice’

Author’s photo