Permeability

If it has holes in it, water will find a way through it. ​

Water droplet (ju lrun) Pixabay

This is true for your tent, your roof, and your garden. In fact, permeability is pretty much the name of the game when it comes to plants and soil.

The rate at which water flows through something else is called permeability. If you’ve ever tried buying a home, you were probably required to pay someone to conduct a perc test. Real estate percolation tests are done to make sure that your house won’t wash away when it rains and that your septic system won’t back up into the living room. A percolation test In the garden can help plants get the water and nutrients they need without drowning. Before we learn how to conduct a perf test, let’s find out why it’s important.

Water in the soil

In the garden, water and air flow in and out of soil, leaves, and even individual plant cells. For a plant, this is the Stuff of Life. The water and air that flow in and out of a plant’s cell walls carry sugars, minerals, oxygen, carbon dioxide, hormones, waste products, and chemicals that allow your plants to thrive or die. [If you’ve ever battled poison ivy or poison oak on your property, you can use a leaf spray that gets absorbed through the stoma (sort of like pores) and carried down to the roots through the phloem. The chemical kills the plant at the roots. This only happens because of the permeability of the leaves.]

Now, too much of a good thing is a bad thing. Without adequate permeability, your plants will drown, suffocate, dehydrate, or starve. Not good. Healthy soil is made up of different size bits of sand, loam and clay. The spaces between these bits are called macropores and micropores, depending on their size. Air and nutrient-rich water pass through these spaces, feeding and nurturing your plants. If the spaces are too small (or absent), plant roots cannot get to the food and air they need to live.

So, how can you, as a gardener, improve the permeability of your soil?
    • avoid overwatering
    • aerate compacted soil
    • apply mulch and compost
    • avoid walking on wet soil

Signs of permeability problems:
    • mud
    • standing water
    • hydrophobic soil
    • chlorosis (loss of green color)

How to conduct a percolation test for soil permeability:

1. Dig a few holes six inches wide and one foot deep.
2. Fill the holes with water.
3. After the holes drain completely, refill with water.
4. If the total drainage time is longer than four hours, your soil has poor permeability.

Ideally, you will want the water to drain at a rate of one or two inches per hour. Of course, sandy soil will drain much faster, taking valuable nutrients with it. You can improve the holding capacity of sandy soils by adding aged manure or compost. If your soil contains more clay, like mine does, you can improve permeability by adding… you guessed it - aged manure or compost! Compost and aged manure add organic material to the soil, creating a wider variety of sizes of both soil and spaces. This variety allows for healthier growth and drainage.

Paved areas can lead to drainage and permeability problems. Permeable paving materials solve this problem by creating a firm surface for walking and parking while still allowing water to seep through. Permeable paving materials are affordable and attractive. They can also eliminate weeds growing up between paving stones!

Do your garden a favor by learning about permeability and composting!