The following article is courtesy of tropical plant and soil expert Lynn Griffith.

Marc McCoy recently posted a terrific blog about tissue testing in turfgrass. Great job, Marc! I thought I would follow up with a blog about leaf analysis in ornamental plants, as the process is somewhat different.

The terms “tissue testing” and “leaf analysis” are used interchangeably by many in the industry. I know that some growers think of “tissue testing” as plant disease analysis. I therefore prefer the term “leaf analysis”, but whatever floats your boat.

First, a little advice about sampling. Leaf nutrient content varies with leaf age. Very new, tender flushes are in a state of the developmental flux, and tend not to be very reliable in generating crop response. Sampling older leaves might tell you what the nutritional status was a year ago, which we don’t care about so much.

Most all leaf sampling in ornamental plants involves the most recent fully matured leaf. Select the youngest leaves on the plant which are fully sized and fully hardened up. Collect leaves from a number of different plants in the block, avoiding edges and row patterns.

Check out the video Media Sampling in the Nursery to learn more.

For most labs, a good-sized handful of leaf tissue is plenty. It doesn’t hurt if the leaf sample dries between the time you collected and the time it arrives at the lab. Nutrient contents won’t change. What you do want to avoid is leaf samples that begin to rot. As leaf tissue starts to decompose, say in a plastic bag, the nutrient contents in the sample can change considerably.

You are best off putting leaf samples in paper bags, though you can use soil sample bags or plastic bags if you ship the samples very promptly with overnight or second day shipping. I find Flat Rate Priority Mail from the Post Office works well and is inexpensive. In my experience, most all of the shipping companies do a good job.

Nutrient content in different ornamental species can vary quite a bit. A hydrangea and an oak tree have very different ranges where the nutrient levels should be. The difference can sometimes be double or triple for some nutrients. It is therefore very important that your lab uses the correct leaf analysis rating standards when calling a nutrient level high or low. For example, a leaf nitrogen value of 2.4% would be fine for an oak tree, but deficient for a hydrangea.

Using the correct leaf analysis rating standard is critical for interpreting test data and maximizing crop response. Some labs do a lousy job on this. I recently sent in a sample of a “hybrid tea rose”. My numbers were rated as “tea olive”, a completely different plant with different nutrient requirements.

For less common ornamental varieties, rating standards may not exist. When that happens, I try to go to a better-known plant in the same family for interpretation guidelines. It matters a lot!

Regarding interpretation, there are a couple of things to watch for. Number one, you can’t always trust that the iron in a leaf tissue sample is available. This is especially true in monocots. Plants can take up iron in unavailable forms, so you can have a very chlorotic plant with medium or even high iron levels, and yet the plant is really deficient in iron.

Check out the video Interpreting Test Results from Media Samples to learn more.

Sometimes, when plants are growing very rapidly, a leaf sample will show in the deficient range. The numbers in the leaf analysis are a percentage of the dry weight of the tissue. When plants are growing very rapidly, the dry weight expands quickly. We call this phenomenon “growth dilution”. It is especially common with nitrogen.

I have seen about a half million leaf analyses in my career. I look at not only the values, but also the ratios of certain nutrients. Not all experts believe that nutrient ratios are important, but I do.

Many times, when relating a leaf analysis to symptoms in a crop, the raw numbers will not identify why. When that happens, the answer to why a crop looks the way it does can often be found in the nutrient ratios. I like using a leaf analysis, as it tells you what nutrients are getting into the plant, and in what ratios and quantities. Using a leaf analysis together with a soil analysis will provide you with an excellent window to see into a crop and determine what is going on.

Kindest Regards,

Lynn Griffith