How should I fertilize my vegetables?

ASK THE HORT AGENT

Question How should I fertilize my vegetables?

Answer In 1879, North Carolina became the first place in the world to require any product being sold as a “fertilizer” to have an analysis for the buyer. The analysis had to state the amount of N-P-K (nitrogen-phosphate-potash) in the fertilizer. The person responsible for this requirement was North Carolina’s first Commissioner of Agriculture and former Confederate Colonel Leonidas Lafayette Polk. Now, every country in the world requires this analysis on any product sold as “fertilizer.” http://docsouth.unc.edu/nc/polk90/bio.html

Exactly 130 years after the first bag of “fertilizer” was sold, we still have trouble knowing when and how much to apply. There are two fertilizer recommendations to consider - general and specific.

General recommendations target the nutrient plants use the most – nitrogen. The most common advice is to apply fertilizer immediately prior to planting and then reapply during the growing season. If you have not taken a soil sample recently, then broadcast either 8-8-8 or 10-10-10 on top of the ground. The best rate is 20 or 30 pounds per 1,000 square feet. Till the fertilizer into the soil to a depth of 3 to 4 inches.

Vegetable plants should be side-dressed (a band of fertilizer placed 4 to 6 inches from plants) about midway through their maturity cycle. Sandy soils and periods of excessive rainfall may require more frequent side-dressing applications. For a typical side-dressing application, apply one pound of 10-10-10 or two pounds of 5-10-5 (or 5-10-10) per 100 feet of row.

Crops such as tomatoes, eggplants and okra require two or three side-dressings per season because of their long growth cycles. Beans and peas need to be side-dressed just before flowering. Pepper, squash, and tomatoes need a side-dressing three weeks after transplanting, at flowering and the beginning of fruit set. Cucumber, cantaloupe, and watermelons need to be side-dressed when the vines start to run.

Slow release fertilizers are typically not recommended for vegetable crops because the crops are so short lived. Slow release fertilizers can be used on perennial crops like asparagus, berries, grapes and other fruit.

Specific recommendations can only be made when a soil test has been performed. The results of a soil test will give you the ability to adjust the second and third number (phosphate and potash). For example, instead of 10-10-10, a different analysis may be recommended (like a 10-15-0 or 5-0-15).

A soil test will also address pH and the amount of lime needed to adjust it properly. If your pH is low, then your vegetables won't be able to properly access any fertilizer you add. Other nutrients like calcium and magnesium will also be addressed on the soil test results. Soil samples should be taken at least once every three years.

For more info on fertilizing vegetables visit http://www.ext.vt.edu/pubs/envirohort/426-323/426-323.htm or http://msucares.com/lawn/garden/vegetables/soil/fertilizer.html If you do not have internet access, then call me at 910-893-7533 or email at gpierce@harnett.org

All commissioners of agriculture should be required to grow a beard like pioneering Col. L. L. Polk. http://en.wikipedia.org/wiki/Leonidas_L._Polk

Gary L. Pierce

Horticulture Extension Agent

Harnett County