Fertilizing The Vegetable Garden Shouldn't Be Taken Lightly

UNIVERSITY PARK, Pa. -- Preparing this summer's home vegetable garden includes adding fertilizer, but a vegetable expert in Penn State's College of Agricultural Sciences says savvy gardeners started the fertilization process last fall.

"After homeowners till under their garden crops in the fall, they should get a soil test kit and find out what nutrients, if any, the garden needs," says Peter Ferretti, professor of vegetable crops. "If the garden needs a treatment, such as adding lime or spreading manure, the application has the entire winter to work into the soil.

"If you haven't tested the soil this year, you still can do a test and follow its recommendations, but the soil won't have as much time to absorb the nutrients," Ferretti adds.

Ferretti says soil test kits are available for a nominal fee at Penn State Cooperative Extension county offices, as well as many garden centers.

He explains that soil test results will tell homeowners if their soil is acidic, with a pH of 5.8 or lower, or alkaline, with a pH of 7.2 or higher. "If the soil is acidic for vegetables, lime will be recommended for most crops, with the exception of watermelon, rhubarb and greens," Ferretti says. "If it's alkaline, the soil can be acidified by adding iron sulfate, powdered sulfur or aluminum sulfate. Carefully follow the directions for sulfates. Applications should be higher in fall and lower in spring."

Many organic gardeners prefer to use manures instead of chemical fertilizers. Ferretti warns gardeners never to apply manure after crops have been planted. "Manure is home to many food-borne pathogens such as E. coli 0157: H7, and bacteria can be spread to the vegetables by rain, watering or by the gardener," he says. "If you use manure, it should always be applied the previous fall, to give it a chance to break down within the soil."

In years past, soil tests offered three separate fertilization recommendations, depending on the type of crops to be planted. Most labs today, including Penn State's, offer a single mid-range soil amendment.

"If gardeners blindly follow mid-range recommendations, some types of crops will be moderately over-fertilized and other types will need a second fertilizer application about a third of the way into the growing season," Ferretti says.

--Crops that need less fertilizer: Beans, peas, radishes, watermelons and turnips.

--Crops that will need more fertilizer: Cabbage and related crops, tomatoes, sweet corn, beets, carrots, onions, celery and potatoes.

After consulting the soil test recommendations, Ferretti suggests applying fertilizer as soon as the garden soil is workable. Ferretti says 1.5 pounds of a 5-10-5 or a 5-10-10 fertilizer will adequately fertilize a 50-foot crop row with a 6-inch wide band of fertilizer on both sides, or can be broadcast/spread on an area of 100 square feet.

"Never apply fertilizer directly on the plant," Ferretti says. "Ideally, you should apply it about three or four inches from the plant to let the roots absorb the nutrients."

Ferretti says commercially produced organic/inorganic fertilizer mixtures can offer a 4-6-4 mixture of nutrients. Ferretti suggests applying about 20 percent more of a 4-6-4 mixture to reach the fertilization level offered by a 5-10-5 product.

Ferretti also points out that manure that is purchased as fertilizer can vary widely in nutrient content. "Organic manures come from many sources: horses, sheep, swine, poultry and cattle," he explains. "The quality can be variable. In order to know what you are buying, I would suggest testing the manure for nutrient content and then purchase the manure at the same place each time."

If gardeners prefer to purchase bags of manure, Ferretti recommends following the application instructions included on the bag.


EDITORS: For more information, contact Peter Ferretti at 814-863-2313.

Contacts: John Wall jtw3@psu.edu 814-863-2719 814-865-1068 fax

Last Updated March 19, 2009