I also wanted to quick circle back to soil testing, especially since we talked about adding lime around certain plants. I thought I'd share my process and my results with you.
Soil testing is pretty quick and easy. You can get soil test kits from your state agricultural extension office. I got mine here.
For my vegetable garden I took small bits of soil about 6 inches down from about 3 different places in each of my vegetable gardening beds. I put all those bits into a container and mixed it up.
I let the soil dry out for a couple days (just so it would not be so wet and heavy to mail). I filled out the form and added a cup of my soil mix. Then just took it to the post office.
I got my (somewhat surprising) results 6 days later. Here is the result summary.
The potassium (K) is a little low. I have no idea why the calcium and magnesium so high, but from what I’ve read, calcium is one element it’s OK to have in excess. The plants will only use what they need. Since the pH is in the right range, I only have to add fertilizer.
You have to do a bit of math to figure out just how much fertilizer to add. You get the recommendation to add 10-10-10 fertilizer which means the fertilizer contains 10% (by weight) of nitrogen (N), 10% phosphorus (P) and 10% potassium (K). If you look at fertilizer bags, you will see the NPK numbers on the back and standard commercial fertilizers are 10-10-10.
But, I use organic fertilizer in my garden and the numbers are typically much lower and not always the same ratio. So I need to increase the pounds of fertilizer I add to make up for the lower numbers. For example, if my fertilizer is 5-5-5, I will need to put on twice as much. I may also need to add a mix of organic fertilizers to get the right number of pounds of each element. A local nursery can be very helpful for this.
For me, the tricky part is converting the pounds per 100 square feet into how many cups full to add to my 40 square foot raised bed. Honestly, I just estimate based on the weight and volume of the bag (ehhh... that looks like about an eighth of this bag...). Kind of a visual conversion from weight to volume.
One last thing to mention about the results, down at the bottom is a little chart.
You can see the actual pH. 7 is a bit higher than I want, especially for potatoes. I’m surprised by this result and I’m glad I checked before I added any lime to my cabbage and broccoli. I’d really like a 6.5. So I won’t add any lime for the next couple years and then test again.
The other thing to look at is CEC (cation exchange capacity). This is an indication the ability of a soil to hold on to nutrients so plants can get them if they need them. If CEC is below 16, more organic matter should be added to help bring it up.
Overall, it looks like my garden soil is in decent shape with just a few tweaks needed.