Fall Is the Perfect Time to Test Your Soil: How to Take a Soil Sample
Beautiful flowers start long before the first seed is planted.
They start with the soil. I can't stress how important this is.
Fall is one of my favorite times to start planning for the next growing season, and according to Penn State Extension, fall is also the perfect time to take a soil sample.
As I continue expanding the growing space here at Thief of Weeds, soil testing is one of the first things I do before deciding what a new bed needs.
It can be tempting to look at a new growing area and immediately start adding compost, fertilizer, lime, or other amendments. But without knowing what is already in the soil, we're really just guessing.
As some of you know, I am a Penn State Extension Master Gardener. The education I received about soil through the program really opened my eyes to just how important soil health and soil testing are especially for a flower farm.
Soil testing is the foundation for making fertility decisions. Testing in the fall has several advantages: the soil is often moist enough to make sampling easier, the growing season is winding down and, most importantly, you have time to receive your results and make a plan before spring.
If lime is recommended, for example, applying it well ahead of the next growing season gives it time to begin adjusting the soil pH.
So before I start adding things to a new flower bed, I want to know:
What does this soil actually need?
For this process, I follow recommendations from Penn State Extension and Penn State University's Agricultural Analytical Services Laboratory.
What Does a Soil Test Tell You?
Penn State's standard soil fertility test provides information about your soil's fertility and pH and gives you lime and fertilizer recommendations based on what you tell Penn State you plan to grow.
The standard analysis includes information such soil pH, lime requirement, phosphorus, potassium, magnesium and calcium.
That is one of the reasons soil testing is so valuable. Instead of simply knowing a few numbers, you receive recommendations that can help you make better decisions about your particular growing space.
It takes the guesswork out of fertilizing and amending your soil.
What I Use to Take My Samples
You don't need complicated equipment to collect a soil sample.
I use my hori hori knife!
My hori hori works really well because I can push the long blade down into the soil to approximately the depth I need and remove a narrow section of soil.
I also bring along a clean plastic bucket or gallon-sized plastic bag to collect my samples.
For a home garden or cultivated growing area, Penn State's Agricultural Analytical Services Laboratory recommends collecting soil to approximately 6 inches deep.
For my flower farm, I test different growing areas separately. That includes individual beds when appropriate, the native soil beneath new no-till beds, and other areas of the property that have different soil or management histories.
I take a small amount of soil from each location and place it into my clean container.
And here's an important part of taking a proper soil sample:
You don't just take one scoop of dirt.
Take Samples From Throughout the Bed
According to Penn State's Agricultural Analytical Services Laboratory sampling instructions, you want to collect thin slices or cores of soil from at least 13 different locations within the area you're testing.
I move throughout the bed, pushing my hori hori approximately 6 inches into the soil at each location and taking a narrow slice of soil.
All of those small samples go into the same clean bucket.
Why so many?
Because one little scoop of soil might not accurately represent an entire garden bed.
Maybe that particular spot has more compost. Maybe fertilizer was distributed a little heavier there. Maybe one part of the bed is naturally different from another.
Combining samples from throughout the growing area gives the laboratory a much better picture of the soil you're actually growing in.
If part of your garden has a different soil type, has received different fertilizer or lime applications, or has been managed differently, Penn State recommends testing that area separately.
What About Fruit Trees?
Fruit trees are sampled a little differently.
Penn State's instructions for tree fruit recommend collecting soil cores to approximately 8 inches deep just inside the drip line of the tree canopy.
For a representative composite sample, Penn State recommends collecting soil from at least 15 to 20 locations.
So if you're testing the soil around fruit trees, don't automatically use the same sampling method you use for your flower or vegetable beds.
Mix Your Soil Samples Together
Once I've collected soil from throughout the bed, I thoroughly mix all of those small samples together in my clean bucket.
Those individual samples are called subsamples. Once they're combined, they create one composite sample that represents the entire growing area.
This is important because the soil you ultimately send to the lab should represent the whole bed—not one particularly good or bad spot.
Air-Dry the Soil
Penn State recommends spreading the mixed soil out on newspaper and allowing it to air-dry overnight in a warm room.
Don't put it in the oven or try to speed up the process by heating it.
While the soil is drying, break apart larger clumps and remove stones or other obvious debris.
Prepare Your Final Sample
Once the soil has dried, mix it again and take approximately 1 cup of soil from your composite sample.
That is the soil that gets submitted for testing.
If I'm testing several beds or growing areas at the same time, I make sure every sample is clearly labeled so I know exactly which test results belong to which bed.
You definitely don't want to get those mixed up!
I like to give each sample a simple name that will still make sense to me when the results come back, such as, new 30-foot flower bed, dahlia bed, perennial cutting bed, fruit tree area.
Complete Your Penn State Submission Form
Penn State has different soil-test submission forms depending on what you're growing, including home gardens, flowers and landscape plants, commercial crops, turf, fruit and other growing situations.
Be as specific as possible about what you're growing.
That information matters because Penn State uses it when developing the lime and fertilizer recommendations included with your results.
Soil-test kits can be purchased through Penn State Extension county offices and from some commercial firms or garden centers.
You don't actually have to purchase a kit, though. Penn State also allows you to print the appropriate submission form online and send your soil in your own plastic bag or other suitable container.
As of this writing, Penn State's standard soil fertility test is only $10 per sample.
For the amount of information you receive about your soil, I think it is one of the best investments you can make in your garden.
How I Package and Mail My Soil Samples
When I'm ready to send my soil samples to Penn State, I keep the process very simple.
I put the dried soil for each sample into a gallon-sized plastic bag and clearly label the outside of the bag with the name of the bed or growing area it came from.
If I'm testing several areas at once, each soil sample gets its own separate bag and label.
I then place all of my labeled soil samples into a shipping box along with my completed Penn State soil-testing submission form.
Before I close the box, I make sure the names or identification numbers on my soil samples match the information I've written on the submission form.
This is especially important if you're sending several soil tests at the same time. You want to be able to look at your results later and know exactly which report belongs to which growing area.
Send Your Sample to Penn State
Samples can be mailed to:
Penn State Agricultural Analytical Services Laboratory
720 Tower Road
University Park, PA 16802
Once your soil has been analyzed, you'll receive a report showing your results along with recommendations based on what you're planning to grow.
And this is where soil testing really becomes useful.
Instead of wondering:
Should I add lime?
Do I need more phosphorus?
Should I fertilize this bed?
Am I adding something my soil doesn't even need?
You have actual information to help you make those decisions.
Why I'm Doing This in the Fall
For me, fall soil testing fits perfectly into preparing the flower farm for another season.
The flowers are winding down, new beds are being prepared, and I have time to make decisions based on actual test results rather than rushing to amend soil right before planting.
Penn State Extension specifically calls fall a preferred time for soil sampling.
There are several reasons why:
- Crops and plants are often out of the way, making the area easier to sample.
- Fall soil has usually picked up some moisture, making it easier to get my hori hori into the ground.
- You'll have your results in time to plan fertilizer and lime applications for the following growing season.
- If lime is needed, you'll have time to make that application well ahead of the next crop.
Instead of getting to spring and wondering what I should add to a bed, I can go into winter already knowing what my soil needs and make a plan.
As I continue adding more growing space here at Thief of Weeds, I want to build those beds intentionally.
For me, soil testing gives me that starting point.
Because beautiful flowers don't begin when I plant the seed.
They begin with the soil.
And that's really the whole point:
Test first. Amend second.