For my last column before I leave for my new assignment in Northwest Missouri, I decided to think about what one tip would be best to leave you with. There are, of course, a number of things that can go wrong in raising a horticultural crop, so there are many tips to choose from.

I took a look at the titles of my newspaper columns through the years, and there’s one topic that I can’t seem to get away from, because it keeps surfacing all the time: soil pH.

A soil with a properly adjusted pH is not guaranteed to be problem free. But a soil that is too acid or alkaline for the plant you are trying to grow is almost guaranteed to cause problems. The plants are under continual stress. Diseases and insects seem to plague your efforts. Nutrients are not taken up well. So by properly evaluating your soil’s pH, and then correcting it per your soil test’s recommendations, you will go a long way towards eliminating a lot of potential problems.

Fall is a good time to get a soil test. Soil amendments such as lime and especially sulfur take time to work, and by adding them to your garden now, you will hopefully have an ideal soil pH by next spring when you’re ready to plant your garden.

Soil tests assay for several factors, including your soil's pH. If the soil is too alkaline or too acid, the plants will not do well, even with added fertilizer. The reason is that plants have a preferred pH range, and if your soil does not fall within that range, nutrient uptake by the plant will be affected, even with adequate supplies of nutrients.

Most garden plants need a pH between 5.5 to 6.8, which is slightly acid. 7.0 is neutral on the pH scale. Left alone, many soils in Missouri tend to become more acid through time, and thus lime is needed to raise the pH. But this may not automatically be the case, and a soil test is always advisable. Applying lime to an already alkaline soil will only make the problem worse.

Some plants, such as azaleas and blueberries, prefer an acid soil. Adding lime to soils where these plants are growing can cause major problems. I especially recommend a soil test in these situations. Often sulfur will need to be added to the soil, and a soil test will tell exactly how much is needed.

In a garden soil, where we are constantly watering, adding fertilizer, removing crops, and incorporating crop residue, the pH can vary due to these practices themselves. For example, some fertilizers may acidify the soil through time. On the other hand, if the irrigation water is alkaline, this tends to raise the soil pH. People who add wood ashes without testing the soil can raise the pH to excessively high levels. Thus, it's a good idea to have your soil tested every few years, to insure that your soil pH is not getting into an undesirable range.

After testing the soil, you may need to add either lime or sulfur, if your pH needs adjustment. For acid soils lime is added. If the pH is too high, sulfur is added. In either case, try to obtain finely ground materials, since they break down faster, and will change your soil's pH more quickly. The soil test will indicate the amount of lime or sulfur to use.