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Senior Information Specialist
University of Missouri Cooperative Media Group
Published: Tuesday, Jan. 31, 2012
David H. Trinklein, 573-882-9631
COLUMBIA, Mo. – A healthy garden starts from the ground up.
University of Missouri Extension specialists encourage gardeners and homeowners to remember the most important ingredient of a fruitful harvest: soil.
“Soil is the basis of good plant growth,” said David Trinklein, MU Extension horticulturist. “If you start with good soil, you all of a sudden become a much better gardener than if you start with poor soil. If you treat the soil properly and develop a good root system, everything else becomes easier.”
As garden patches lay fallow through winter months, gardeners can seize the opportunity to test and prepare for planting this spring.
While commercial producers often test soils yearly, Trinklein recommends that most gardens be tested every three years.
Sample soil in a zigzag pattern across your garden patch, avoiding berms or depressions where nutrients may pool. Create a separate sample when situations vary due to soil quality, sunlight or what you want to grow.
“Simply spade about 7 inches deep and take 2 inches out of the center of that spade,” Trinklein said. “Combine a number of samples into a bag, mix well and take out about a cupful that can be taken to your county extension center or sent to a soil testing lab.”
Soil test results will come back with recommendations based on what you are growing, including how much of what nutrients to add.
Three major nutrients – nitrogen, phosphorous and potassium – can have the most impact on gardens. These often come as fertilizer blends of 5-10-5 or 12-12-12. (These numbers represent the percentage of nitrogen, phosphorous and potassium, in that order, contained in the fertilizer mix.) While percentages may not add up to the exact needs for a garden’s soil, it is best to get as close as possible.
Trinklein says the source of nitrogen is important. Most plants prefer fertilizers with nitrogen from nitrates. Ammonium sources like urea – the least expensive nitrogen-imparting fertilizer – have to be converted in the soil first into the nitrate form of nitrogen. That does not happen unless soil temperatures rise above 60 degrees, so early spring gardens might not get a boost from fertilizer before it washes out of soil. Check fertilizer labels to verify nitrogen source.
“If they had their druthers, most plants would prefer nitrogen in the nitrate form,” Trinklein said. “Certain species like tomatoes are extremely sensitive to excessive amounts of ammonium, and I’m sorry to say that many labeled ‘tomato fertilizers’ contain urea, which converts to ammonium.”
After planting, apply soluble fertilizer to heavy feeders such as tomato every seven to 10 days for optimal growth. Soluble fertilizers provide nutrients that are immediately available for uptake by roots, while granular fertilizers can lag in their impact because they first need to break down and dissolve.
Soil structure also contributes to a healthy garden. When adding nutrients recommended from a soil test, add organic matter to the soil. This can be compost, well-decomposed manure, sphagnum peat moss or a combination. Organic matter gives the soil good structure, allowing for better drainage and nutrient-holding.
“Most Missouri soils are very low in organic matter, and it’s a best management practice to incorporate 4 inches of well-decomposed organic matter in one’s garden every year,” Trinklein said. “We’d like ultimately to see 5 percent organic matter.”
Add nutrients and organic matter right before you plant in spring to ensure fertilizers don’t run off and pollute ground water.
Trinklein cautions gardeners to not jump the gun and work their soil too soon.
“One of the worst thing gardeners can do is work the soil when it’s too wet,” he said. “It takes years and years of best management practices to build good soil structure. We can very quickly destroy that by getting in with our new rotary tiller and beating the soil into submission when it’s too wet.”
An easy test can tell gardeners whether they can till.
“Take a sample of soil from the top, form it into a ball the size of a baseball and put it in the palm of one’s hand. With the heel of the other hand, strike that rather firmly. If you can see the imprint of the heel of your hand it’s too wet, but if it crumbles and flies apart it’s perfect.”
Contact your local MU Extension office to learn more about soil testing fees or read more at www.extension.missouri.edu/G6950.
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