Sidedressing Garden Vegetables
For many vegetables, it is not recommended to supply all of the garden plant’s nitrogen needs at the beginning of the season. High nitrogen rates can lead to large, bushy plants but poor fruit set and vegetable yield.
Also, nitrogen, the most essential element needed by most garden plants, is water soluble and can be flushed down out of the plant’s rootzone by regular watering. Applying a portion of a vegetable’s nitrogen needs up front and then applying an additional ration of nitrogen later in the growing season is recommended for many garden crops and is referred to as “sidedressing” or “topdressing”
The amount of nitrogen needed, if any, later in the season varies from crop to crop.
K-State horticulturists provide the following recommendations for a few common garden vegetables. Recommendations are in pounds per 100 foot of row of a common high-nitrogen fertilizer such as 27-3-3, 30-3-4 or 29-5-4 (the first number being the nitrogen percentage in the fertilizer product). As a rule-of-thumb, one pint of fertilizer weighs approximately one pound.
Sweet Corn: One pound per 100 foot of row early when corn plants are 8 to 10 inches tall, and again when the sweet corn has tasseled. One week after tasseling apply one pound of fertilizer per 100 row foot. If using an ag-grade urea 46-0-0, that rate can be reduced a little more.
Tomatoes: Three applications of nitrogen are recommended for tomatoes during the season. The rate is the same for the corn, one pound of a high nitrogen fertilizer per 100 row foot. If you only have a few plants, apply 1 tablespoon of a 27-3-3 (or something similar) per plant.
The first sidedress application on tomatoes should be made one to two weeks before the first tomato ripens. Then again two weeks after picking the first ripe tomato. The third application of nitrogen fertilizer should be made one month after the second sidedressing, or six weeks after the first ripe tomato is harvested. This will provide late-season nutrition to keep the plant going as long as it can into the late summer and fall. This is most important for indeterminate tomato plants that produce fruit season-long.
Again, if only fertilizing a few tomato plants, apply about 1 tablespoon of fertilizer per plant each time. Most lawn fertilizers contain about 20 to 32 percent nitrogen and will work fine for sidedressing your garden, but make sure the fertilizer does not contain an herbicide. Do not use a “weed and feed” fertilizer product on the garden or injury to the plants will likely occur.
Pumpkin: Apply one tablespoon of nitrogen fertilizer per plant when vines start to run.
Peppers and Eggplants: Apply one tablespoon of nitrogen fertilizer per plant after first fruit sets.
Potato: Apply 1 ½ tablespoons of nitrogen fertilizer per plant after tuber formation begins.
Not all garden crops need to be sidedressed with nitrogen. Excessive nitrogen on sweet potatoes, watermelon, carrots, beets and parsnips can reduce yield or lower quality. No additional late-applied nitrogen is recommended on these crops.
A complete list of vegetable sidedressing recommendations can be obtained from the local Extension office.
