Living SoilHow much did you spend on soil, fertilizer and amendments last year? Now: how much of it did your soil actually need?
Most gardeners cannot answer the second question, and that is not a criticism. Nobody tells you. The bag says to feed, so you feed. The neighbor says lime, so you lime. A soil test is how you stop guessing.
Why bother testing?
The research puts it bluntly: failing to test can lead to under or over fertilizing, which can damage plants, pollute storm water and waste money. Adding lime or a phosphorus fertilizer without knowing what the soil holds can create nutrient imbalances that hurt plant health.
Here is a pattern worth recognizing. A common mistake is piling on phosphorus year after year, simply because the bag says 10-10-10. When a test shows phosphorus is already high, the advice is no phosphorus fertilizer for a few years, until a test asks for it. Compost, especially compost made with manure, carries phosphorus too, which is one more reason to check.
When to test
References differ on how often. One guideline says every 3 to 5 years, or whenever problems show. Another recommends testing beds and vegetable gardens every year. Pick a rhythm and stick to it, and always test before you change pH or start a new feeding plan.
Timing within the year matters too. Do not sample just after you have added lime, fertilizer, compost or manure, or when the soil is very wet or very dry. All of those skew the result.
How to take a sample
- For beds and vegetables, dig down about 6 inches.
- Take 8 to 10 small samples from across the area, not just one spot.
- Mix them together into one composite sample.
- Send roughly a pint of the mix to the lab.
Lab or home kit?
Home kits are usually less accurate than a lab, and their accuracy varies by nutrient. They are roughly fine for pH and useful as a starting point, but they do not give tailored recommendations.
Reading the results
- Optimal, excessive or very high means more than enough. Adding more will not improve growth.
- Phosphorus above optimum means skip it. That is when a fertilizer with a zero or near zero middle number makes sense.
- pH in range means no lime. If your pH is already acceptable, there is no benefit to liming.
- Nitrogen is the odd one out. Soil tests for nitrogen are unreliable in humid climates, so nitrogen advice usually comes from the plant type and the soil's organic matter instead.
Different labs use different phosphorus test methods with different ideal levels, so read your result against the range printed on your own report, not someone else's.
What to do with it
A test tells you what your soil is missing. The next step is supplying it at the right rate for the plant. If your test says pH is too high, the guide to raising and lowering pH explains the options. And when you enter a lab result into Living Soil, it adjusts its advice for pH, lime and where phosphorus or potassium are high or low.