Soil testing: The process at the North Carolina state soil lab

The inch and a half of snow we got from the Blizzard of 2014 is melting today (by Sunday, it should be 60 degrees). It was fun and pretty while it lasted, but now that large patches of  mud are visible between the–drifts?–of snow, I’m thinking about spring.

Spring means soil testing for me this year, as I didn’t get my samples in before the fall cutoff. Due to high volume of sample processing, the state has begun charging a fee for samples submitted between December and March. It’s otherwise a free service, and while the fee is a mere $4, it’s the principle of the thing.

soil test for quince bed

A soil test report for one of my garden beds, taken last winter.

I’ve often wondered what happens at the soil lab. We send off a box of dirt, and we get back a detailed report showing levels of nutrients, organic matter, and pH, and recommendations for improvements based on what we plan to grow in each plot or bed sampled. And then the other day, I happened across this video, and my questions are resolved.

Growing a Greener World is an excellent series broadcast on many local PBS affiliates, or you can watch them online.


Azalea chlorosis

Or, Why Are My Azalea Leaves Turning Yellow?

Most of the subjects of the Great Azalea Migration have settled in well. I pruned them directly after this year’s flowering to give them more shape. Waiting too long to prune risks cutting off next year’s flowers.

This one, however, is showing signs of displeasure.

chlorotic azaleas yellow leaes green veins

Notice how the leaves are more yellow than green, but the veins remain dark green? This is a sign of chlorosis, a condition in which the leaves don’t produce adequate chlorophyll. The source of the problem lies in the soil’s pH; if the pH is not appropriate for the plant, that is, if the pH is too low (acid) or too high (alkaline), the plant’s roots cannot take up the nutrients (in this case, iron) in the soil. The solution to such a problem, therefore, is not to dump fertilizer on the plant, but to test the soil’s pH to confirm the diagnosis and then adjust it accordingly.

Azalea Growing Conditions

Azaleas like acid soil, typically in the pH range of 4.5 to 6. My soil falls within this range naturally. But it is possible that when this shrub was transplanted, some lime got mixed into the compost by accident; or it might have happened when I planted some smaller perennials at its base. Azaleas also want a shady location, or one that receives some morning sun. The light exposure is not the problem here.

This condition is interesting to me, because as you can see the older foliage is perfectly green. I would have thought the problem would be more evenly distributed on the plant.

So I will try to get a soil test for this patch of ground in the coming week or so. And if you are very good, I will show you the results and the remedy.

Another glimpse of spring

Today, the 60F temperatures beckoned me outside again, if only to take a few more soil samples in between meetings and other work to be done. Tomorrow, we are told, we should expect sleet.

So I watched this fellow for awhile.

cardinal and windchime

The best part about winter gardening in the south is the clear, brilliant blue sky. Even when it’s cold, skies this blue keep the winter blahs at bay. A bit.

nice profile

Still, I am ready for spring.

Soil testing 101: How to prepare a soil sample


This gallery contains 5 photos.

Soil testing is not sexy. It’s like eating my spinach. I know it’s good for me; I know I should do it; but it’s just not the first (or second, or tenth) thing I want to do right now…But the best time to do it, I say, is when you can get around to it. Better sometime than never. It’s a free service and the task is not onerous. Here’s what you need to do. Continue reading