Soil Not Absorbing Water

Did you know that soil is naturally hydrophobic? That's right, once soil dries out it it can become difficult to rehydrate.

If the soil contains peat moss or coco peat, such as seed-starting or planting mix, this can be doubly true. Peat moss and coco peat are especially hydrophobic when dry.

Not to worry, though!

Rehydrating soil that's not absorbing water is easy - it just takes a little time and patience. Here's what you need to know about hydrating dry dirt:

Why Does Dry Soil Not Absorb Water?

When soil dries out and becomes hydrophobic, you may notice that water just runs right off and doesn't saturate the dirt.

This can be common in dried-out planters and grow bags - you try to water only to have all the water pour right out the bottom without absorbing.

Dry soil in garden plots can reduce your gardens ability to absorb rainfall when it happens. This can create a negative feedback loop whereby dry soils can't handle the water which they do receive, and dry out even further.

This is especially common in desert regions or the contrast between extremely dry soil and extremely intense seasonal rainfall events maybe stark. These situations can become dangerous very quickly.

Hydrophobic Soil

Moist soil is quick to soak up water, because of water's adhesion to other water through capillary action.

Conversely, when soil becomes hydrophobic and dries out, it fills with air and repels water. Water droplets cling to each other but have difficulty infiltrating small pores in soil.

This effect can be compounded in clay soils where pore space is smallest.

Problems With Hydrophobic Soil

In planters and soil blocks, hydrophobic soil is little more than a nuisance. Slow rehydration will resolve the issue.

At a larger scale, however, dry hydrophobic soils can cause huge problems when they clash with large rain events.

Here in the desert Southwest, soils are often extremely dry and hydrophobic. When it does rain in the desert, it frequently happens all at once over a short period.

This can lead to catastrophic flash flood events as the dehydrated soil has lost all capillary action, and therefore, all ability to absorb water quickly.

I saw less flooding when I lived on the East Coast (50" of rainfall / year) than I've seen in the Sonoran Desert (11" of rainfall / year). This is because East Coast soils are rarely dry enough to prevent absorption when it rains.

East Coast soils have an incredible ability to soak up and retain moisture during large rainfall events like a sponge.

By contrast, desert soils can be much more prone to flash-flooding when they dry out and their water infiltration rate plummets.

Stay safe around dry soils when there's flooding on the forecast! This can be extremely dangerous in combination. Stay away from low-lying areas, washes, and canyons.

How to Rehydrate Dry Soil

Now that we know what causes dry soil to repel water and become hydrophobic, let's figure out how to solve it.

If you need to rehydrate soil, patience is the virtue for you.

Try one of these methods:

Bottom Watering

If you're dealing with planters, soil blocks, cell trays, or grow bags, bottom watering is a great way to let dry soil soak up moisture slowly.
Be patient, and eventually the soil will rehydrate on its own.

Irrigate Slowly

If you run drip lines, you've got the ability to rehydrate soil slowly with little effort. Just set your drip lines to run for short durations numerous times throughout the day. This will let the soil soak up the moisture little by little without flooding it.

If you've got the ability to change your drip line pressure, consider lowering the PSI if you need to slowly rehydrate soil - you'll get a slower flow rate. If you do this, though, just be sure that water still makes it all the way to the end of your lines! (ask me how I know)

Hand-Water Slowly

When all else fails, you can hand-water your soil slowly to rehydrate it. The drier it is, the slower you'll need to go at first.

Hand-water little by little, making sure to go slow enough that the water doesn't start to run away from ya.

You can also plug a hose into a raised bed or garden plot, and turn it on very low and let it run a while. Make sure the hose is buried under the mulch layer, and keep an eye on it to prevent overflow. The lower the hose is turned, the more time you're giving the dry soil to soak up the moisture.

Watering underneath the mulch layer like this helps it to absorb better and reduces evaporation - especially important in arid climates.

A hose nozzle with a fine showerhead also works wonders in helping to rehydrate hydrophobic soil.

For indoor planters, cell packs, and soil blocks, a pump sprayer works great. Just spray down your soil a little at a time, waiting a couple minutes in between for it to saturate.