Healthy soil will encourage healthy plants. If soil is deficient in nutrients such as iron, plants will be more susceptible to pests and diseases, requiring more time and expense for optimal production. By simply adjusting the pH in the soil and adding supplements, your soil will produce healthy plants almost effortlessly.
Check the pH in your soil with a pH tester probe (about $20 at garden centers) to first determine if there is an iron deficiency. Simply insert the probe into the soil to get an accurate reading. Average pH levels register 6.8 to 7. A primary symptom of iron-deficient soil is plant leaves turning a yellowish color and stems become spindly. This indicates a lack of pH balance, a measure of soil acidity or alkalinity, and possibly a need for supplemental nutrients.
Apply an iron supplement if the soil's pH is higher than average to reduce the alkalinity and improve performance of plants installed in the area. Annuals such as flowers, vegetables, and some herbs will only require about 2 tbsp. per 100 square feet of garden soil while trees and shrubs may require more. Each product will specifically define the rate of application on the product label.
Apply ferrous sulfate or chelated iron, a type of iron (examples include ironite and iron sulfate), and spread the proper rate according to package directions. Work this into the soil with a rake or just water in.