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August 22nd, 2012

Nitrogen-Depleting Mulch

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?

blog-dougAs 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

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July 17th, 2012

Embrace Your Brown Lawn

With all the hot weather we’re having in Iowa, my bluegrass lawn looks kinda brown. Would a summer feeding help it to green up?

blog-dougWhen a lawn is stressed from heat, fertilizer is the last thing it needs. Cool-season turf grasses, including bluegrass, fescues, and perennial rye, slow their growth in response to hot weather. If the weather is dry as well as hot, you’ll notice a lot of brown blades among the green. This summer “dormancy” can last through Labor Day or until cooler weather and fall rains prompt a return to green.

You could keep the lawn green through summer with copious amounts of water. But I would argue against that sort of wastefulness. Instead, why not take a break from mowing and allow the lawn to go dormant?

There’s one caveat to letting the lawn brown out, and that is the chance that patches of turf will die if the weather stays dry for too long. A good soak every 2 or 3 weeks is all it takes to keep bluegrass alive. Depending on your soil type and how dry the soil is to begin with, it could take between one-half inch and one inch of water to soak the ground to a depth of 6 inches. If natural rainfall fails to provide this much, you’ll have to step in. Apply water in the early morning, when less will be lost to evaporation, and water slowly so every drop sinks in.

Other summer strategies for keeping a lawn healthy include setting the mower blade high—up to 4 inches—and using a mulching blade that drops finely chopped clippings back on the lawn.

Save the fertilizer for fall. Bluegrass and other cool-season grasses naturally regenerate in fall, when temperatures drop and soil moisture is more abundant. In fall, bluegrass will devote the extra nutrients to extending and thickening its root system instead of producing more top growth. Choose a slow-release organic product.  —Doug Hall

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May 9th, 2012

Choosing Organic Fertilizers

Please define organic where using superphosphate is concerned. Also when using 10-10-10. Thank you.

blog-dougSuperphosphate is a synthetic chemical fertilizer that is not approved for use in organic agriculture. It is manufactured by treating mined phosphate rock with sulfuric acid. It’s toxic to the microbial life of your soil. Because it’s water soluble, it can also contribute to phosphorus pollution of waterways.

If your garden soil lacks phosphorus, it’s better to apply it in the form of bone meal, rock phosphate, composted poultry manure, or compost made from yard waste and kitchen scraps. These organic materials release phosphorus to the soil slowly as they are broken down by soil bacteria. Fish emulsion and liquid seaweed fertilizers offer a quick phosphorus boost.

The ratio 10-10-10 describes the quantities of nutrients within a fertilizer but doesn’t reveal whether or not it’s organic. That said, the vast majority of fertilizers with a 10-10-10 analysis are synthetic. The three numbers represent the percentages of available nitrogen, phosphorus, and potassium in the fertilizer.

Gardeners who are in the habit of regularly feeding their soil with rich compost often find that they have no need for additional fertilizers. If necessary, you can supplement compost with complete organic fertilizers that blend natural sources of nitrogen, phosphorus, and potassium, as well as micronutrients such as iron and calcium. You’ll know which products at the garden center are organic by their “OMRI Listed” label.  —Doug Hall

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April 17th, 2012

The Best Soil for Strawberries

My order of 50 bareroot strawberry plants will arrive at the end of April. The supplier recommends mixing 10-10-10 chemical fertilizer into the soil. Can you suggest an organic alternative? I have some horse manure, but it doesn’t appear to be fully rotted to use at this time.

blog-dougStrawberries grow best where the soil is fertile, well-drained, and amply enriched with organic matter. If you have been using compost, organic mulches, and cover crops in your garden for several years, you may need to do nothing further before planting the strawberries. A soil test will give you an accurate reading of how fertile your soil is.

If your soil falls short of the ideal, I recommend you dig in some organic amendments before you plant. Composted horse or steer manure is excellent for this purpose; it’s sufficiently composted when it looks and smells like soil. Yard-waste compost is another good source of nutrients and organic matter. Sphagnum peat moss as a soil amendment adds organic matter but little in the way of nutrients. Ideally, you should prepare the soil a few weeks before planting the strawberries.

Water thoroughly after planting, then give each plant one cup of a half-strength fish emulsion solution or compost tea to jump-start growth. Follow up 3 weeks later with another application if growth is slow.

Let your supply of fresh horse manure decompose longer before using it. You can layer it with leaves, kitchen scraps, and other garden debris to make compost, if you wish, or simply let it age in a pile. Next spring, use it to top-dress the strawberry bed when the plants begin to bloom.  —Doug Hall

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December 13th, 2011

Sugar as a Soil Supplement

Someone told me that sugar is good for plants. I sprinkled some around my vegetable garden this year but didn’t notice anything different. How much should I apply?

blog-dougPlants don’t need you to add sugar to their soil; they make their own. Through the process of photosynthesis, which is powered in nature by energy from the sun, plants turn water and carbon dioxide into sugars. Plants use their self-made sugars as a fuel for growth and reproduction.

Sugar you add to the soil will instead feed soil microorganisms, such as bacteria and fungi. These naturally occurring microbes are nature’s recyclers; they help to nourish plants by breaking down the bits of organic debris in soil into their nutrient components—including the potassium, magnesium, nitrogen, and other elements that are essential for plant life. In this sense, sugar could benefit the plants in your garden by boosting the microbial population, thereby speeding up the rate at which nutrients become available.

But plants already have a process for encouraging microbial life. Soil scientists have discovered that plant roots exude sugars—sugars produced by photosynthesis—as a way of developing mutually beneficial relationships with microbes. By controlling the types and amounts of sugars they release, plants can select which kinds of microorganisms will colonize the soil around their roots. Not coincidentally, plants choose to feed the microbes that will provide them with the nutrients they need most. Compared to this sophisticated à la carte system, a sprinkle of processed sugar from your pantry is just junk food for bacteria.

By the way, there’s another reason some gardeners haul the sugar canister out to the garden. Sugar added to the planting holes of vegetable transplants is said to discourage root knot nematodes, a destructive soil-dwelling parasite that plagues many Southern gardens.  —Doug Hall

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