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How Often Should You Fertilize a Vegetable Garden?

By Susan Lundman ; Updated September 21, 2017

You're off the hook for fertilizing a vegetable garden in late fall and winter when vegetables typically no longer need extra nourishment. But depending on the plants you grow, you do need to fertilizer from spring through late summer or early fall. When you give vegetables the right amount of fertilizer, you get healthier plants and increased crops.

Soil Testing

Healthy soil, high in organic matter or aged manure, reduces the amount of fertilizer you need and allows you to customize the fertilizer to meet your garden's needs. Test the soil for its chemical and pH makeup before you begin a vegetable garden and every two to three years after that. Garden stores and nurseries sell test kits for chemical analysis or can direct you to laboratories that accept soil samples through the mail.

Begin soil testing by determining whether you have sandy, loamy or clay soil. Form a ball with moist soil in your fist; sandy soil doesn't hold its shape at all, clay soil holds fast and loamy soil falls apart only slightly.

Soil Adjustments

After identifying the soil texture and chemical blends in the soil, make these improvements:

  • Add about 1 pound of compost, aged manure or ground bark to each square foot of clay soil to loosen its texture. Add the same amount to sandy soil to increase its water-holding capacity.
  • If the soil pH is very acidic, add a product with limestone, commonly calcium carbonate, using 28 pounds for each 100 square feet for sandy soil, and 46 pounds for loam or clay soils.
  • For very alkaline soil, add 4 pounds of sulfur to each 100 square feet of sandy soil, 5 pounds to loamy soil and 6 pounds to clay soil. Use lesser amounts for only slightly alkaline soil.

Fertilizer Basics

Use a balanced, complete fertilizer as a foundation for vegetable garden soil. Look for a label that indicates equal amounts -- for example, 12-12-12 -- of the main ingredients in fertilizers: nitrogen, phosphorus and potassium, or N, P and K. Add about 2 pounds of dry fertilizer for each 100 square feet in the garden, working in 1 pound of fertilizer 6 inches into the soil before planting and spreading the second pound about four weeks after you plant.

Types of Applications

Fertilizers come in both granular and liquid forms, and you have choices when adding them to a garden:

  • Top Dressing. Apply dry fertilizer by hand, scattering it around the base of plants out as far as the drip line or to the end of the outermost leaves where water drops off.
  • Side Dressing. Place dry fertilizer in a narrow furrow you've created with a trowel or hoe along the side of vegetable rows. Side dressing allows you to quickly and easily fertilize a long row.
  • Base Application. When you pour liquid fertilizer on the soil under plants, diluted or not depending on the instructions,  you get the fertilizer right where you want it. The method works especially well for container vegetables.
  • Foliar Fertilizing. Spraying a liquid fertilizer on the leaves works best when you want to deliver a specific nutrient to a specific vegetable, such as iron to a veggie with yellowing leaves.

Know Your Plants

Different kinds of plants need varying amounts of fertilizer applied at different time, but most benefit from the basic balanced formula initially and a mix high in phosphorus applied every month or six weeks during the growing season. Certain kinds of plants need special treatment:

  • All vegetables, including seeds and seedlings, need the basic application of fertilizer about four weeks after planting.
  • Transplanted vegetables need a fertilizer with lots of phosphorus to stimulate root growth. Use a mix such as 8-32-16, mixed with water, and apply about 1/2 cup around the base of each plant.
  • Annual and biennial vegetables are those that produce only one crop, with annuals maturing and producing in one year and biennials taking two years to mature before producing. These veggies, which include beets, carrots, kale, parsley and Swiss chard, need the basic two fertilizer applications plus an additional two applications of a high-phosphorus applications such as you use for transplanted crops.
  • Perennial vegetables, such as asparagus or rhubarb, need more fertilizer than annuals because their roots are alive year-round. Increase the amount of a balanced fertilizer for these vegetable to 20 pounds for each 1,000 square feet of growing space.
  • Heavy feeders, such as corn and tomatoes that have a long growing season, need lots of nutrients. Give these veggies another two applications

    of a granular or water-soluble balanced fertilizer in the same amount as the basic application, spaced one month apart throughout the growing season.

 

About the Author

 

Susan Lundman began writing about her passions of cooking, gardening, entertaining and recreation after working for a nonprofit agency, writing grants and researching child development issues. She has written professionally for six years since then. Lundman received her M.A. from Stanford University.