Roses are red and violets are blue... tomatoes like acid soil and zinnias like it to be alkaline. If the plant you're growing doesn't have the right type of soil pH, you must test and amend your soil with appropriate nutrients before you plant. You'll need to do a little homework to learn the reading of your soil pH and also to learn the preferences of the plants you want to grow.
Test Your Soil
Inexpensive soil test kits are available at garden centers and nurseries---they make it quick and easy for you to test your soil to determine whether it is acidic, neutral or alkaline. The pH of soil is measured on a scale ranging from 0 to 14: neutral soil is in the center, at about 7.0, while readings lower than that are considered acidic and those that fall above are alkaline. Many vegetables prefer slightly acidic soil, and other plants such as geraniums do best in soil that is alkaline.
Lowering Soil pH
To lower soil pH and make your soil more acidic, add sulfur or an acid-based fertilizer. For every square yard of garden space, mix 1.2 oz. of ground rock sulfur into sandy soil if you want to reduce your pH by one point. For other types of soil such as clay, add more sulfur---3.6 oz. per square yard is recommended by TheGardenHelper.com. They add that including composted leaves, sawdust, cottonseed meal, peat moss or wood chips will also reduce soil pH.
Increasing Soil pH
To raise soil pH and make your soil more alkaline, add hydrated lime. For every square yard of garden space, add 4 oz. of hydrated lime to sandy soil, eight ounces to loamy soil, 12 oz. to clay soil and 25 oz. to peaty soil. Don't expect instant results---it can take as long as one year for your soil to readjust and give a higher pH reading when you test it.
Good Drainage is Vital
All plants, except water plants, need their soil to be well drained. Well drained means simply that water flows through it quickly and never leaves a puddle for more than a short time. Imagine if you were forced to sit or stand with your feet in a bucket of cold water---this would be an uncomfortable situation, just as it is for plants that don't like to have their root systems constantly soggy. You can easily improve soil drainage by adding organic materials such as compost, rotted manure, leaves, sawdust, wood chips, grass clippings, peat moss and other materials to your poor drainage areas. High Country Gardens advises using a ratio of about one third compost to two-thirds garden soil. Raised beds that contain large quantities of organic materials are also very helpful for improving soil drainage.
Sandy soil can also provide poor drainage in the opposite direction: water runs through sandy soil too quickly and doesn't give the roots enough time to drink up all they need. Adding organic materials to sandy soil is also the solution to improving its fast-draining characteristic.