If you have a vegetable garden, flower beds, house plants, outdoor planters, trees, a lawn, a pasture, or agricultural crops, whatever it might be, soil nutrition is essential. One of the best ways to monitor the nutrients in your soil is by using a soil probe to extract a sample for lab or home testing.
Soil probes are versatile, valuable tools for anyone who grows plants. They let you core out a soil sample which can then be sent to a lab or tested with a home test to measure nutrient levels. They can also let you know when your plants need watering and help loosen soil that has become packed.
To learn more about how valuable a soil probe can be, how to use one, and how to choose a quality one, read on!
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What are Soil Probes?
Soil probes are slender, hollow rods with a cutting edge and a handle. They’re designed to withdraw cylindrical soil core samples at various depths. Soil probes can also punch aeration holes and/or sample soil moisture levels at multiple depths.
Soil probes work by cutting through the soil with a sharp edge of a long hollow pole which is generally 6 – 36 inches long and ¾ of an inch in diameter. This sharp edge allows the probe to cut through either loamy or clay soil. Some soil probes make cutting through heavier or harder soils easier with a spiral, auger-like section above the cutting edge or a pointed, bit-like attachment.
Step probes have bars to the side to step on to push the probe soil deeper. These might help you dig deeper to see what nutrients your soil has.
As there are different types of soil, there are also different types of soil probes. For example, if your soil is damaged from an environmental disaster, you might want a longer probe to see how far the damage goes down.
Here are the different types of soil probes and what they do:
- Handheld soil probes, the most common, take shallower samples
- Soil augers, also handheld, take deeper samples
- Post-hole diggers take wide samples
- Hydraulic soil probes are mounted on trucks or tractors and can be used for deeper samples
- Other soil probes sample wet soils, sediments, turf. Some soil probes are used to find buried tanks, pipes, or cables.
As you push the soil probe into the soil, it collects a sample inside the hollow tube. These tools provide a few ways to access the soil sample. On some soil probes, the cutting edge is slightly smaller in diameter than the tube. Consequently, the soil sample fits loosely inside the soil probe’s tube.
Other soil probes have open slots going up the sides of the tube, allowing you to view the sample taken at different depths, which is especially useful for judging soil moisture.
Some probes have a hinged cover over a slot in the tube near the cutting edge. The cover opens like an alligator’s jaw which let’s you view the soil sample.
Fun fact: Since the hinge opens like an alligator jaw, the opening is called an alligator or gator opening.
Another type of soil probe has a “bulldozing” rod inside the hollow tube. As you push the probe into the ground, the soil sample pushes the bulldozing rod, or sample extractor, higher up into the tube. A knob in the center of the probe’s handle attached to the extractor is also pushed upward.
When you’re ready to eject your sample, you simply push down on the knob causing the extractor to move the soil sample out of the hollow tube.
If you plan on taking your sample to your local cooperative extension agency, you can insert liners into the soil probes. The sample is then collected inside the liner, making it easy to transport and transfer to the representative at the extension agency.
Some manufacturers offer soil probe attachments that can be purchased separately.
The available attachments include:
- Cutting tips for different types of soils and surfaces
- Tube extensions for taking deeper samples
- A sample extractor
- Adjustable bars to turn the soil probe into a step probe
How Deep do Soil Probes go?
Soil probes can go as deep as the probe is long. The Cornell Cooperative Extension of Warren County, New York recommends 0 to 6 inches (0 to 15 cms) for gardens, crops, and grass but 8 to 16 inches (20 to 41 cms) for trees.
The North Carolina State Cooperative Extension recommends 28 to 32 inches (71 to 81 cms) for deep soil nutrient management.
Soil probes are the most effective way to collect soil samples for testing. They collect enough soil for sampling without creating invasive larger holes, and samples are easy to remove from the probe.
Soil probes generally cost anywhere from $50 to thousands of dollars. Post-hole diggers are inexpensive and readily available. Handheld soil sample probes also are readily available and moderately priced between $50 and $100.
Sturdier soil augers for deeper samples are more expensive, but hydraulic probes are the most costly and most difficult to find.
Some of the best soil probes are durable and rust-resistant. The sample should be easily accessible and easy to remove. The soil probe should also be effortless to thoroughly clean to prevent mixing soil when taking soil cores across various depths.
Soil probes come in several different models and sizes.
- The soil probe handle should allow you to use as much of your body weight as possible to push the probe into the soil. A step-probe provides a way to add more weight and force to push the soil probe into the ground.
- A t-shaped handle makes it easier to use the probe, and rubber grips on the handle make using the soil probe more comfortable.
A soil probe with a changeable tip to cut through various soil types makes a soil probe more versatile.
Interchangeable soil probe tips are made from various materials, including:
- Chrome-plated chrome-molybdenum
- Stainless steel
Chrome plating improves the rust resistance of chrome molybdenum. Nickel plating provides a hard surface that resists wear and corrosion.
Stainless steel combines rust resistance, durability, and easy cleaning.
We recommend the stainless steel Varomorous 21″ Soil Sampler Probe from Amazon.com. It has a t-shaped handle that provides a good length for pushing the probe into the soil.
To collect a soil sample for nutrient testing, you’ll need to collect 10 to 15 shallow sub-samples and 10 to 15 deeper sub-samples.
- Take the sub-samples in different areas of your garden, flowerbeds, field, lawn, pasture, or around your trees. The sub-samples should come from relatively uniform areas.
- Sample an area of exceptionally rich or poor growth separately.
- In areas with no tilling or minimal tilling, samples should be taken at depths of 0 to 6 inches (0 to 15 cms) for gardens, crops, and grass areas but 8 to 16 inches (20 to 41 cms) deep for trees.
- In tilled areas, take samples at the tilling depth, usually 6 to 10 inches (15 cm to 25 cms).
- Mix the shallow samples in one container.
- Mix the deeper samples in another container.
You’ll need 2 cups of soil samples (473 ml) for each testing area.
You should take soil samples and have them tested every two to three years. However, if you replant multiple times during the growing season, annual testing might be needed.
Avoid taking samples of wet soil if you can. However, if you must sample damp soil, spread the soil sample out on sheets of newspaper and dry it at room temperature before testing it.
You can take samples any month, but take them at about the same time as in previous years to be consistent. Samples are usually taken before the next planting season, in the fall before the ground freezes or in the spring after the ground thaws.
Taking your samples in the fall allows you to amend or improve your soil before planting. This is particularly important if your soil is highly acidic and needs the addition of lime, sometimes referred to as calcium or calcium-magnesium compound.
Lime takes two to three years to become thoroughly mixed into your soil, but if you add it in the fall, you can see an improvement over the winter and early spring months.
Your local cooperative extension service can probably test the pH level of your soil in their office. If so, you could get their recommendations on adjusting your soil’s pH levels in as little as three days.
Tests of soil nutrient levels are generally sent to a lab, which will mail the results to you in one to two weeks. If you don’t want to wait for a lab and prefer to do home testing, we recommend the following home tests from Amazon; just note they will not be as accurate as sending your samples to a lab:
- Recommended kit – LaMotte 5679-01
- Test kit with an app – MySoil – Soil Test Kit
- Affordable kit – Luster Leaf 1601
For vegetable gardens, flower beds, lawns, or trees, your extension service will need to know the following information before making their recommendations for your soil:
- The characteristics of the site
- The types of grass, flowers, vegetables, or trees you grow
- The age of trees and perennial plants
- The fertilizer you use
- If you apply manure, how often you apply it, and the quantity used
For cultivated agricultural crops, the service will want to know:
- The map symbol and the name of the soil from the cooperative extension services soil survey
- The depth to which you till the soil
- The crops you want to grow
- The crops you have grown in the past
- The cover crops you grow
- If you apply manure, how often you apply it, and the quantity used
The information in your soil analysis report depends on whether you requested a pH test or a soil nutrient test.
A pH report lists the pH level of your soil. A soil nutrient report lists the level of nutrients in your soil depending on the selections you made when you requested the information. The University of Maine offers a downloadable PDF file entitled “Interpreting Soil Test Results for Gardens and Grounds.”
The pH report lists the pH level of your soil on a scale from 0 to 14. A rating of 7 is considered neutral. Soils with levels above 7 are considered alkaline, and those with levels below 7 are considered acidic.
Most plants grow best in soils with pH levels of 6.2 to 7.2. Levels above or below those recommended for your plants can interfere with your plant’s ability to absorb nutrients.
If your pH level is at or below 5.8, you’ll receive a buffer pH report that estimates the amount of lime you need to add to your soil to bring it up to a reading of around 7.0. The buffer pH report also may include instructions regarding:
- The number of applications needed
- The amount of lime that should be applied per application
- The amount of time that should pass between applications
Your report may also include information about:
- The levels of soluble salts in your soil
- Excess levels of lime
- The amount of organic matter in your soil
- The percent base of your soil’s saturation
- The cation exchange capacity (CEC)
The percent base saturation measures the supply of certain nutrients in your soil and the balance between them. This measurement is related to the pH level and the CEC, which can be an indication of high fertility.
The CEC indicates how well your soil stores and releases nutrients to your plants. It, too, is dependent upon your soil’s pH level.
Depending on your area, the testing options might include a nutrient report on the following:
- Phosphorus (P)
- Zinc (Zn)
- Iron (Fe)
- Manganese (Mn)
- Copper (Cu)
- Potassium (K)
- Magnesium (Mg)
You may find other nutrients listed as well. If your soil needs amending, the report will include recommendations for which nutrients to apply as well as how many applications are required and how much of each nutrient to use.
Soil probes help you maintain the nutrients in your soil and prevent plants from becoming too wet from overwatering or too dry from lack of water. Once you have one, though, you may find yourself using it to find drainage tiles, sprinkler leaks, and a whole lot of other valuable tasks you never imagined doing.