Right after I finished mulching my rose garden with free wood chips I got from a tree service, I read that wood chips suck all the nitrogen out of the soil. Should I fertilize now?
As soon as you spread mulch, there’s a population boom of bacteria, fungi, and other soil microbes that work to decompose organic matter. These beneficial organisms consume some of the nitrogen present in the soil. The nitrogen loss is temporary, however, because the nitrogen is once again available to plants when the microbes die.
But in the meantime, the thin layer of soil that is in direct contact with the mulch will relinquish some of its fertility. The depletion of nutrients does not extend deep into the soil, so it won’t likely affect anything other than the shallowest-rooted annuals.
The benefits of organic mulch outweigh the possibility of a temporary nitrogen shortage. Mulch conserves moisture and contributes to a healthy root zone. It also helps to suppress weeds. As mulch decomposes, the nutrients held within it—including a small amount of nitrogen—are released.
For roses and other plants with high nutrient needs, it’s a good idea to keep an eye out for nitrogen deficiency, whether you’ve mulched with wood chips or not. Plants lacking nitrogen grow slowly and exhibit pale or yellow-green leaves; in extreme cases, growth may be stunted.
To preclude the chance of nitrogen deficiency, many gardeners make a habit of distributing a small dose of slow-release nitrogen fertilizer every spring to roses, perennials, edible crops, and other heavy feeders. Good organic sources include alfalfa meal (about 5 percent nitrogen by weight), fish meal or fish emulsion (5 percent), blood meal (12 percent), and feather meal (15 percent). Compost and worm castings also contain small amounts of nitrogen. —Doug Hall
I have lots of kitchen scraps (eggshells, coffee grounds, fruit and vegetable peelings) but cannot figure out how to develop compost out of it. Everything I’ve read says to add green and brown such as dried leaves and green grass to it. I need to figure out some sort of ratio. But how?
Books have been written on the topic of making compost; my current favorite is Compost Gardening by Barbara Pleasant and Deborah L. Martin. It represents a wealth of wisdom and practical experience on a topic that, when it comes down to it, is really quite simple. The decomposition of organic matter into compost is going to happen whether you’re measuring and manipulating the materials in a pile or not. “Compost happens,” as the tongue-in-cheek bumper sticker says.
The ratio you’re referring to is the balance of carbon-rich materials (or “brown” ingredients, such as straw, shredded paper, sawdust, and dry leaves) to nitrogen-rich materials (the “greens,” including your kitchen scraps, manure, and fresh grass clippings or weeds). In theory, a proper balance of these ingredients makes for a fast and efficient compost pile. In practice, however, most gardeners add whatever organic debris we have on hand to our compost piles without giving much thought to the carbon-nitrogen ratio. We end up with compost, too, even if it takes longer than it would with a perfectly managed pile.
You can layer your kitchen scraps with dry leaves or other “browns” in a pile or bin. Or you can try pit composting, a technique that involves digging holes or trenches in the garden (often between rows of vegetables or in fallow areas of the garden), depositing your kitchen scraps in the ground, and immediately covering them with soil. The scraps break down quickly—and you don’t have to worry about getting the ratio right.
For more information about how to make and use compost, you’ll find a great collection of articles and videos on this website. —Doug Hall
I’m not sure what to do with all my excess wood ash from the fireplace. I need to lower my soil pH, so I can’t add the ash to the garden or compost.
The ash from a wood-burning fireplace contains nutrients that plants need, including potassium, calcium, and trace amounts of zinc, magnesium, and phosphorus. But those nutrients come with a warning: Wood ash is strongly alkaline. If added to soil, it will raise the pH, or the measure of a soil’s acidity or alkalinity. Where the soil is too acidic (pH too low) and a higher pH would be beneficial, wood ash can be applied to lawns or gardens in place of agricultural lime to raise the pH. But if you are dealing with a neutral or alkaline (high pH) soil, adding wood ash would be a mistake.
The same goes for adding wood ash to a compost pile. Consider including wood ash as a compost ingredient only if the pile contains significant quantities of acidic materials, such as shredded oak leaves or pine needles. Even then, apply the ash with restraint, because too much can result in a loss of nitrogen from the compost. At a higher pH, the nitrogen present in the compost pile will escape to the air as ammonium hydroxide; if you smell ammonia near your compost pile, it’s losing nitrogen.
If you decide you shouldn’t use wood ash in your garden or compost, and you can’t find a farmer or gardener who can use it, I suggest you send the ash to a landfill with the rest of your household waste. —Doug Hall
The other day, an Organic Gardening reader emailed us a question about whether or not he should add shredded newspapers to his compost pile. (My opinion: Shredded newspaper is OK in moderation, especially in piles that are blessed with too much nitrogen and need some extra carbon-rich materials to balance it out. In my garden at home I’m more likely to utilize newspapers in an unshredded layer under the mulch, where they have a compounding influence on the mulch’s beneficial effects.)
The reader’s question inspired me to start a list of items that shouldn’t be added to a compost pile. Weeds that have gone to seed; meat scraps from the kitchen; used cat litter: Some things are obviously unwelcome as compost ingredients.
Others require some research. Wood ash, for example, is often considered a safe compost ingredient—in small quantities. But it is highly alkaline and raises the pH of the decomposing pile, allowing nitrogen to be released into the air as ammonia gas. Not just smelly, but a waste of an essential plant nutrient.
In the end, I came up with 10 items that are best kept out of the compost bin. Look for the list in the Skills & Abilities section of the June/July 2011 issue of Organic Gardening. —Doug Hall