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Garden Maintenance: Feeding and Fertilizer

Fertilizer falls into three basic categories: organic, inorganic, and a combination of the two. As you may have guessed, organic is completely natural, and inorganic is manufactured.

Generally speaking, all fertilizer is composed of the three main nutrients that plants need: nitrogen, phosphorus and potassium. These nutrients are referenced by the letters N, P and K respectively on fertilizer packaging. For example, you may see fertilizer packaging that reads N P2O5 K2O. You may also see phosphate, which corresponds to phosphorous, and potash, which corresponds to potassium.

Potash and rock phosphate are mined. Inorganic fertilizers are manufactured from petroleum and natural gas, which the exception of superphosphate and triple superphosphate, which are concentrated from rock phosphate using acid. That said, you can decide whether to use something completely natural and harmless on your plants, or something synthetic manufactured from petroleum products.

Fertilizer is used either as a base, topdressing or liquid. Using it as a base means that you sprinkle it into the hole before planting a given plant. Using it as a topdressing means that you tamp some on the ground around the plant.

Organic fertilizer is usually slow-release, meaning that it delivers nutrients over a long period of time. Most inorganic fertilizers are fast-release, though a few are slow-release. Fast-release fertilizer should be applied more frequently in smaller doses.

Here’s a rundown of different fertilizers and their uses:


  • Bone meal: 2-5% nitrogen; 20-30% phosphorous with some calcium. Slow-release. Apply in spring or fall. Contains lime. Be sure that it’s marked as sterilized.
  • Dried blood: 9-14% nitrogen. Used as a topdressing or liquid feed. Helpful for leaf vegetables. Fast-acting. Apply in late spring or summer.
  • Fish meal: 4-9% nitrogen; 7% phosphorous; 1 to 2% potash. Base dressing. Slow release.
  • Seaweed extract: 2% nitrogen; 1% phosphorous; 4-13% potash. Liquid feed. Gentle and fast-acting. Improves winter hardiness.
  • Wood ash: 5-10% potash. Top dressing. Young wood produces the richest ash. Store in a dry place to retain potassium content. Keep off leaves to prevent severe scorching.


  • Magnesium sulfate, otherwise known as Epsom salts: 10% magnesium with sulfur. Topdressing. Prevents and cures chlorosis, which is chlorophyll depletion that causes the plant to lose color.
  • Ammonium nitrate: 35% nitrogen. Liquid feed. Don’t mix this with lime.
  • Sodium nitrate: 16% nitrogen with trace elements. Topdressing. Fast-acting. Note: quickly washes out of soil; keep off of leaves.
  • Calcium nitrate: 15% nitrogen with calcium; contains 48% lime. Topdressing. Long-lasting and fast-acting. Helpful for acidic soil. Can speed up decomposition of compost heap.
  • Ammonium sulfate: 20% nitrogen with sulfur. Topdressing. This is the best source of nitrogen. Increases soil acidity. Don’t mix with lime. Fast-acting.
  • Ferrous sulfate, or iron and sulfur: Topdressing. Treats chlorosis. Increases soil acidity.
  • Potassium sulfate: 48% potash. Base or topdressing. Best source of potassium. Fast-acting for flowers and fruit. Acidifies soil.
  • Superphosphate: 13-20% phosphorous. Base dressing. Best source of phosphates. Keep off of leaves. Don’t mix with sodium nitrate.
  • Urea: 46% nitrogen. Liquid feed.


  • Broad-leaved evergreen fertilizer: 4% nitrogen, 6% phosphorous; 4% potash. Base or topdressing. Fast-acting inorganics combined with slow-release organics. Lowers soil pH.
  • Bulb fertilizer: 4% nitrogen, 10% phosphorous. Base or topdressing. Mostly slow-release organics. Apply when planting in fall, and in mid- to late spring as topdressing.
  • Rose fertilizer: 6% nitrogen, 6% phosphate, 4% potash with iron and magnesium. Topdressing. Fast-acting. Apply in summer. Formulated especially for roses, but you can also use it on flowering shrubs.
  • Iron tonic: 6% chelated iron, 4% sulfur. Liquid feed. Cures yellowing provoked by alkaline soil or iron deficiency.
  • Tomato fertilizer: 8% nitrogen, 24% phosphate, 8% potash. Base and topdressing. Apply as topdressing when fruits appear.

You should note that inorganic fertilizers significantly contribute to water pollution, especially those that are fast-release. That’s because they’re high in phosphorous. This phosphorous is leached into groundwater, which then drains from your watershed into nearby streams, rivers and lakes. The phosphorous leads to nutrient overload in bodies of water, which leads to algae blooms. The lack of oxygen decreases water quality, suffocating fish and other aquatic species.

The cheapest fertilizer you can use on your vegetables and flowers is compost, made right in your very own yard! Here’s a basic and easy composting recipe:

  • 3 parts brown: dry leaves, dry grass clippings, pieces of small brush and twigs.
  • 2 parts green: fresh fruit and vegetable scraps, fresh grass clippings, flower and shrub trimmings, young weeds
  • 1 dash of soil

Mix all the ingredients once a week. Within a few weeks, you’ll have rich soil-type compost that you can add as a topdressing around your flowers and vegetables. Of course, you can add more yard waste and fresh fruit and vegetable scraps as often as you like. Just turn the compost regularly. When you’re ready to fertilize your plants, just dig near the bottom of the pile to extract the rich soil-like material.

There are many other types of completely organic and inexpensive fertilizer, such as rabbit manure and worm castings. “Worm castings” means “worm poo!” Worms work their way through tons of compost, and their excrement is exceptionally rich fertilizer.

Regardless of what type of fertilizer you use, follow directions on the package. Consult your local garden store owner for which types of fertilizer work best on which types of plants and the soils in your area.

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