Soil and Fertilization

Fertilizing your garden can seem terribly confusing. When you go to your garden center there are mountains of bags. Which one is best? What’s the difference between organic and synthetic? How often do I need to use it and how much should I put down? What does pH have to with it? One this page, we’ll take a good look at these questions and crack the N-P-K code without having to get a degree in chemistry.

Soil Test

It is always a good idea to start with a soil test. They can be purchased at your local garden center and they are fairly accurate. If you’d like a more detailed reading, I’d recommend sending a soil sample to your local cooperative extension service. They can send you a soil testing kit with instructions on how to collect the sample and a questionnaire to let them know how you intend to use the garden. A vegetable garden will have different nutrient requirements than a native meadow for example, that will require little or none. After analysis they will send you a report and alert you to any mineral deficiencies in your soil. They will also make recommendations on how to correct them. Knowing exactly what to apply, and not using too much fertilizer makes the small price of testing very worthwhile.


Any fertilizer you buy will have three numbers on it such as 5-5-5. The numbers represent the “N-P-K” ratio, the available nutrients contained in that fertilizer.

  • Nitrogen (N) helps plants grow strong healthy foliage
  • Phosphorus (P) helps roots and flowers develop and grow
  • Potassium (K) or potash is important for overall plant health

Synthetic Versus Organic Fertilizers

Synthetic fertilizers are water-soluble and can be taken up by the plant almost immediately. This can be an advantage if plants are failing and need a quick boost. However, applying too much synthetic fertilizer can “burn” foliage and damage your plants. Please remember this, more is not better! More plants have been killed by kindness in the form of excessive applications of synthetic fertilizers than died because of too few nutrients. Synthetic fertilizers will do little to improve your soil’s long-term structure or fertility. Because synthetic fertilizers are highly water soluble, they can also leach out of the soil and pollute streams and ponds so please use them with caution.

For the long term health of your garden organic fertilizers and compost are the best and safest to use. Generally speaking, organic fertilizers release about half their nutrients in the first season and continue to nourish your soil in subsequent years. They also improve your soil structure, and your soils ability to hold moisture and nutrients. Sandy soils in particular can benefit from the addition of organic fertilizers, or from the use of organic matter like well-rotted compost and manure. Over fertilizing with organic fertilizers is virtually impossible and best of all, it is always safe for people and pets.

The pH or Potential Hydrogen

Now for a little bit of chemistry, let’s look at soil pH. The pH or Potential Hydrogen, of your soil measures whether your soil is acidic (pH <6), neutral (pH 6-7) or alkaline (pH>7) sometimes called sweet. Some plants have evolved to grow in acidic soil like our native azaleas and blueberries. Some plants prefer a sweeter soil like asters, Joe-pye weed, and sunflowers. When you have your soil tested the lab will tell you what the pH of your soil is. Generally speaking, if you chose plants that are native to your area chances are good they’ve evolved to grow in the soil you have in your garden. The obvious exception is new building sites where top soil has been removed. Your local cooperative extension service will take your soils pH into consideration when they make recommendations.