How to Choose & Use Plant Food

Perfect soil has lots of nutrients, but who starts out with that? In the meantime, we fertilize! Some vegetables have huge appetites, and all veggies and most herbs like nutrients early on, when they are making fast new growth.

Whatever food (also called fertilizer) you choose, follow the label instructions on how much to use. Too much can be worse than too little! For example, overfed tomatoes often grow to be huge, yet bear only a light crop late in the season. Use the list below as a starting point for what to expect.

Light Feeders »

These plants like a small amount of plant food to begin, but the greens need regular feeding if you treat them as cut-and-come-again crops harvested weekly.

  • Bush beans
  • Lettuce
  • Mustard greens
  • Peas
  • Southern peas
  • Turnips

Moderate Feeders »

These plants often need good drainage and moisture-holding mulch more than they need feeding. Avoid using organic fertilizers made from processed manure when preparing the soil for beets, carrots, and other root crops. Manure can contribute to scabby patches on potato skins and forked roots in carrots and parsnips.

  • Beets
  • Carrots
  • Okra
  • Pole beans
  • Potatoes
  • Sweet potatoes

Heavy Feeders »

These are often highly productive plants. Mixing in granular, slow-release fertilizer before planting assures a baseline level of feeding. Heavy feeders also respond to extra liquid feeding during the season. Some gardeners prefer liquid only, but more often.

  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Cantaloupe
  • Cauliflower
  • Corn
  • Cucumbers
  • Eggplant
  • Kale
  • Kohlrabi
  • Onions
  • Peppers
  • Rhubarb
  • Squash
  • Tomatoes
  • Watermelon

What is in Plant Food?

Plant food is, indeed, food for plants—the building blocks of growth. A plant food, or fertilizer, has three numbers listed in order on the package that state the percentage (by weight) of the three nutrients plants use in the greatest quantity—nitrogen (N), phosphorous (P), and potassium (K). For example, Bonnie Herb & Vegetable Plant Food is labeled 8-4-4, which indicates 8 percent nitrogen, 4 percent phosphorous, and 4 percent potassium.

Nitrogen (N) fuels new growth. A little is great, but too much causes problems.

Phosphorous (P) promotes root growth and increases blooms. This is a very important nutrient, especially as plants start out.

Potassium (K) is essential to overall health. It helps plants withstand stress from extreme weather and disease.

Other Nutrients »

These are often present in the soil or in amendments such as compost, and therefore not included in plant food.

Calcium (Ca) improves vigor and growth of young roots and shoots. A shortage contributes to blossom-end rot on tomatoes, peppers, and squash.

Magnesium (Mg) helps regulate the uptake of other plant foods and aids in seed-making. It is also important for dark green color.

Sulfur (S) encourages vigorous growth.

Other elements are used in very small amounts, but still essential. Iron (Fe) is often lacking in poor soils. Iron helps turn sunlight to energy and helps leaves stay dark green. Manganese, boron, zinc, copper, and molybdenum are sometimes present in plant food, too. Chlorine and cobalt are also needed for plant growth but are rarely added to plant food.

Types of Plant Food

Plant Food is sold in two main forms: granular and liquid. Granular fertilizers are solid granules for sprinkling. Liquid fertilizers are water-soluble powders or liquid concentrates that mix with water to pour.

Granular is slow, while liquid is fast. There is a place for both in your garden.

Granular Plant Food »

Water-soluble fertilizers give an instant boost, while granular fertilizers need a while to dissolve or decompose before releasing nutrients. It usually takes a few days after watering to see results from granular food. The best way to use granules is to work them into ground before planting. Second best is to sprinkle around the plants.

Slow-Release Granular Food »

These coated granular products have "slow-release" (also called "timed-release" and "controlled-release") properties, meaning they feed slowly over a period of time, usually 2 to 9 months, depending on the formula. Even though their price is higher, they can be more economical if not over-applied. They also are less likely to contribute excess nutrients to any runoff that ends up in local streams.

Liquid Plant Food »

Liquid fertilizers are water-soluble powders or liquid concentrates that you mix with water to make a solution to pour around the plants or spray on the leaves.

Liquid fertilizer is almost instantly absorbed, so plants get the benefits immediately. Nutrients generally last 1 to 2 weeks. Liquid fertilizer is great as a starter solution at planting time and for a quick boost during the growing season for heavy feeders. It’s ideal for potted plants, because the frequent watering needed for containers can also leach nutrients. With liquid fertilizer, you can fertilize as needed when you water.

Tip from Experience »

If plants don’t have all the essential nutrients, they won't grow well. A benefit of adding compost made from garden and kitchen scraps to your soil is that it supplies many of the needed elements. Add compost to the ground or raised bed each time you plant. Over time, your soil will improve.

Posted in: Growing Basics