How to Use a Soil Probe
One of the primary issues in keeping plants happy and healthy long term is in regulating soil moisture. How can you get a sense of the consistency of the soil in a sealed container? Using your finger works for the top few inches of soil, and chopsticks are a cheap way to give you an idea further down, but to really know how wet your root zone is a soil probe is the best solution. These low-fi beautiful tools have been known and loved by professional horticulturists for decades, and are excellent method to understanding the condition of your soil throughout the planter, giving you vital information on when it is time to water.
How to take a soil reading
Assessing soil moisture can be a challenge, especially when working with larger plants and attempting to get a sense of how dry the soil is deep within the pot. Overwatering is the most common reason plants perish, particularly in planters without drainage holes. The soil probe is arguably most useful to use before you water to ensure the soil has reached the desired level of dryness before adding more moisture.
Using the soil probe is easy. Simply insert the pointed end into the soil and push as deep as you can, then slowly pull up. This will take a sample of the soil at several layers allowing you to see and feel the moisture levels throughout the pot.
For most houseplants you'll want to make sure that the soil at the bottom of the pot maintains an even and consistent moisture, but is not soaked or soggy. Note that some species prefer to dry out more than others. Research your specific plant's watering needs and use the soil probe to help determine when your plant is ready for more water. Remember that soil near the top of the planter can often be dry to the touch a day or two after watering, as the area around the plant's roots are where the moisture will collect.
Aerating your soil
If you think you have over watered your plant, the soil probe can be used for aeration. Aerating is the process of poking holes in the soil, so that humidity is able to escape and the root system has access to fresh air. Push the probe all the way into the soil and gently remove it, repeating several times throughout the pot to loosen the soil and create air pockets. This will help bring oxygen to the roots and assist in the drying out process. Alternatively the soil can be aerated in the same method if the soil is compacted and water is not distributing evenly. This can be especially helpful for plants that are newly potted or for plants that are root bound.
Cleaning and maintaining your probe
We chose to make our soil probe out of brass because it's an easily recyclable and sustainable material that has the added benefit of being naturally anti-microbial. While it looks shiny and new straight out of the box, the brass will dull over time. If you want to get it looking sparkly and new, rub any brass polish with a rag on the soil probe and you'll notice it will return to its original sheen in short order.
What about moisture meters?
Moisture meters are a cheap and common tool available on the market. Although great in theory, the moisture meters we've tried have yielded very inconsistent and unreliable results.
Moisture meters don't actually measure moisture, but instead respond to the electrical conductivity in the soil. The basic theory is that if the soil is wet, small amounts of electricity are able to pass more freely in the soil. This is known as conductivity.
In practice, it doesn't take very long for moisture meters to stop working. Salts and minerals build up over time, changing the conductivity of the soil which the moisture meter isn't accounting for. If you're not judicious about cleaning the prongs, corrosion will set in permanently damaging the meter, as the prongs are made from poor quality metal. Lastly they don't work in dry soil as there's no conductivity, so they're quite unreliable during the time you need them the most. Through our years of providing plant maintenance in New York City we've found that the manual method of actually feeling the soil by utilizing a soil probe is the best way to determine soil moisture.