When it comes to maintaining organic gardening soil, the main thing to check for is pH level. The pH spectrum ranges from 0 to 14. A pH of 7 is considered neutral while 0 is totally acidic and 14 is totally alkaline (basic). Soil testing is important since certain plants prefer a bit of an acid or alkaline environment to grow. The pH level of organic gardening soil changes due to certain conditions and therefore needs to be monitored regularly.

Most food-bearing plants prefer a soil that is just slightly acidic in the range of 6.3 to 6.8. Crops such as potatoes and strawberries thrive in even more acidic conditions. Plants such as blueberries and cranberries need a soil as acidic as 4.5 to 5.0 in order to grow. Few food crops require a basic soil with a reading of over 7.0, but some flowers such as lilacs can flourish in even a chalky soil.

The main thing that affects soil pH levels is rainfall. Rain drives away basic elements magnesium and calcium while replacing them with the acidic elements aluminum and iron. Heavy rainfall creates a more acidic soil, so soil pH levels should be checked following a heavy rainfall or long drought.

To increase or decrease the pH level of your soil organically, there are various elements you can use. Nitrogen and phosphorous, which are common ingredients in organic gardening fertilizers, increase a soil’s pH level. Other elements that work in this way include calcium, lime and magnesium. In the event that you need to increase the acidity (decrease the pH level) of your organic gardening soil (not uncommon in times of heavy drought), metals such as copper, iron, aluminum, manganese, zinc and cobalt are useful. Symptoms of a soil that is too basic are the yellowing of leaves. This is a sign of a nutrient deficiency which calls for lowering the soil’s pH level.

Organic gardeners should focus on two elements with regards to fertilizers: phosphorous and nitrogen. Potassium is also an important element, though a bit less so than the other two. There is really no single organic fertilizer source that provides ample quantities of both phosphate and nitrogen. As a result of this, it is important to blend multiple fertilizer sources to give your plants everything they need to grow.

There is a difference in the way soil reacts to phosphorous and nitrogen. Excess phosphorous is stored in soil where nitrogen evaporates. For this reason, organic gardeners will always need to supplement their crops with nitrogen, but phosphorous will not always be necessary if enough have built up in the soil. In order to fertilizer your organic garden, you’re going to need to do a little math. For example, a common organic gardening fertilizer recommendation could is 100 pounds of each nitrogen and phosphorous per acre. Let’s say organic gardener Jim has a quarter of an acre of plants he needs to fertilize. This means Jim needs 25 pounds of nitrogen and 25 pounds of phosphorous to put into his soil. If Jim is using a the fertilizer blend fish meal, he’ll be putting about 9% nitrogen and 2.5% phosphorous for each pound he puts into his soil. So if Jim puts 250 pounds of fish meal on his crops, he’ll get about 22.5 pounds of nitrogen and 6.25 pounds of phosphorous.

So as you can see, if Jim applies this fish meal fertilizer, Jim’s job is not done. He still needs 2.5 pounds of nitrogen and 18.75 pounds of phosphorous. To achieve this, Jim can supplement his fish meal fertilizer with bone meal, a fertilizer high in phosphorous but fairly low in nitrogen. Bone meal is 22% phosphorous and 3.5% nitrogen. If Jim adds 80 pounds of bone meal to his crops, he’ll add 17.6 pounds of phosphorous and 2.8 pounds of nitrogen. When added to his fish meal fertilizer, this brings his total phosphorous to 23.85 pounds and his total nitrogen to 25.3 pounds. While that’s not exactly 25 and 25 pounds of each, it’s close enough that Jim’s crops will thrive beautifully.

Bone meal is really the only organic fertilizer high in phosphorous (it has 22% while most others have no more than 2 or 3%). For this reason, all organic gardeners will need to use bone meal on their crops. Fertilizers high in nitrogen in addition to fish meal include dried blood (13%), and animal hoofs and horns (also 13%).