To Fertilize My Garden

Vanity | June 15th 2025 | Jacquerie

[Jacquerie]

When my spouse and I purchased a fifteen-year old home in 2020, we had our work cut out for us. The place wasn’t quite a fixer-upper but that is where is was headed. The household neglect extended to the surrounding grounds.

After much back and forth with a landscape architect, we settled on the design and plants.

In the back and side yards we wanted bottlebrush, podacarpus, wildflowers, black-eyed susan, day lillies, scarlett hibiscus and indian hawthorne.

Soil Analysis

Before ordering the plants, I got up with our county extension agent to discuss a soil analysis. Why spend thousands of dollars for new plants on the silly hope that the soil is suitable for their needs? We live in a subdivision and there is no telling what kind of fill dirt the developer spread around.

The process is easy and cheap. Way too easy and cheap to ignore.

The first task was to gather a few soil samples from around the proposed garden. Next, combine the samples and spread out (Don’t need much; a couple pints will do.) on a flat surface in the sun to completely dry.

Now it is time to fill out the simple paperwork. You tell the lab your intended purpose. For me it was perennial flowers, but you can indicate vegetables, fruit trees, flowering trees, lawn, etc. Back then the fee was, IIRC, ten dollars. I sent the soil sample, lab instructions and check off to the University of Florida Soil Testing Lab.

Results arrived in about two weeks.

Soil Analysis Results

You will be blown away by the detail. Your extension agent will also have a copy of the report. Contact him to discuss and evaluate.

First and foremost is the soil pH. I’m not a master gardener, but I know that unless the pH is within limits, all the N-P-K in the world won’t work. The pH value for the flower garden was thankfully within limits. This was a bonus because most FL soils need lime to increase the pH.

A separate analysis for our four new Crape Myrtle trees in the front yard was a different story. The soil pH was 5.4 and the trees are happiest at a pH of 6.0. How much lime to add? I didn’t know. pH is ranked on a logarithmic scale, so I didn’t have a clue. Fortunately, my extension agent recommended four cups of garden lime around each tree twice a year.

This coming December I will send off another soil sample from around the trees to the UF Lab and see if the pH is right. They seem happy. They’re growing quickly and feature beautiful lavender flowers.

Mixing Your Custom Fertilizer

For the longest time at our other homes I’d visit a garden cener or hardware store in the Spring and buy 40 lbs of slow release 10-10-10 or whatever they had. I didn’t know the square footage of the garden or anything else. Run the irrigation every other day in the summer and mostly ignore plants that didn’t do very well.

In broad strokes, my flower garden analysis recommended (per 1,000 sq. ft.) no lime, 1.1 lbs Nitrogen N, 0.20 lbs Phosphorus P, 0.70 lbs Potassium K, and 0.46 lbs Magnesium Mg annually.

Armed with a 200 ft tape measure I estimated the Garden’s area at 1,440 sq. ft. An online search showed I could buy individual bags of N, P, and K. The Mg was available at my local hardware store.

So what about those numbers on bags of fertilizer? They indicate percentages of N-P-K. The typical 10-10-10 fertilizer means a 40 lb bag has 4 lbs each of N, P and K. Pretty simple.

As opposed to hardware store fertilizer, my new bags were highly concentrated, featuring concentrations of 46-0-0, 0-46-0 and 0-0-60. How much each of N-P-K does my garden need?

Let’s figure out the Nitrogen. The UF Lab recommended 1.1 lbs N per thousand square feet. Here’s the math: (1.1 lb N divided by 1,000 sq. ft.) times 1,439 sq. ft. = 1.58 lbs of Nitrogen annually.

Since I apply fertilizer three times a year (Mar, June, Sep) each application of Nitrogen equals 0.52 lbs.

So the question is: at 46% concentration of Nitrogen, how much of it do I need to obtain 0.52 lbs of Nitrogen? 0.46X = 0.52 lbs X = 1.13 lbs. QED as your Algebra I teacher would say.

Do the same with the other elements and you’ll have a clue as to how to fertilize your garden. Don’t choke.

[Jacquerie]

I wish you had read my post before commenting.

[Diana in Wisconsin]

Yeah, I realize you’re talking more about landscaping. I was blathering about vegetable gardens.

So, nevermind! :)

[Jacquerie]

Okay.

I always enjoy your Saturday Gardening posts.