Friday, August 10, 2018

Reasons Why My Soil Doesn't Get Wet

Last night it gently rained. 0.56" to be precise. That's a decent amount of rain for overnight and most areas of the farm benefited. But I've learned that I need to get down at soil level and check, especially in the veggie beds. 

It came as a surprise to me many years ago that my soil didn't equally accept rain water. Some growing areas soaked up the moist perfectly. Other areas tended to get too soggy, with the water pooling in areas. Yet other spots were bone dry even after a 5" downpour. Closely observing and playing detective, I figured out quite a bit about what I needed to do to have soil that soaked up the rain (or irrigation) and distributed it well. 

Soil too soggy -- Growing veggies over pahoehoe lava, or a concrete slab like I have up by the house, can be done. But the soil can easily become overly saturated. I needed to add coarse young compost, instead of my fine aged stuff. And I needed to provide drainage channels as needed so that pools didn't develop. Tilling into the soil 10% coarse chunky biochar also helped with drainage while tending to even out the moisture content. Not sure why it works, but it does. 

Soil bone dry -- What was baffling was the dry soil after a good rain. Much of my soil is based upon decades of degraded ohia tree debris, which seems to make for very hydrophobic soil. The rainwater drains via channels, leaving 99% of the ground dry. I found that to be incredible. I could pour on a gallon of water and it seemed to soak in normally. But when I took a trowel and scooped the soil, only the top 1/2" - 3/4" was wet. The rest was dry. The water just drained off into invisible channels and disappeared underground. I tried a variety of methods to deal with this problem. This is what works best for me -- compost. Lots and lots of compost. Plus mulch to keep the sun and wind from damaging the soil ecology. 

Today when I checked the garden areas that I have planted, I discovered that one of the taro beds was dry under the mulch. The mulch layer was only about 1/2" thick, so although it does interfere with the rain getting to the soil underneath, the mulch wasn't the primary problem. The problem was that this bed is a  relatively new growing spot, so it hasn't had much soil improvements yet. There's not much organic material in it to capture the rain and hold it. Plus the mulch wasn't thick enough to help retain what moisture it previously had. Since the bed is already planted, I can't rototill in more compost. But I could top dress with 2 inches of fine compost and lightly scratch it in between the plants.....water it off with fresh mulch. So that's what I'm doing this afternoon. 


  1. I was told that mulching keeps the rain from watering the plants. Maybe that's your problem.

    1. You bring up a good point. Some mulches, especially when applied thick, can indeed impede the passage of rain. I noticed this in my own farm when I applied grass mulch too thickly. I also saw this problem when I used multi-layer paper or cardboard as mulch. The problem becomes extremely noticeable when the mulch is applied over dry soil.

      I ALWAYS take care to either thorouggly wet the soil prior to applying mulch, or generously water the garden bed after the mulch is applied. Plus I take the time to pull the mulch aside and visually inspect the soil moisture.

      I recall my grandmother rushing outdoors when a rainstorm started, using a garden rake to pull the mulch away from her veggie plants, thus allowing the rain to soak right into the soil. Then after the shower passed, she'd go out and rake the mulch back into place. She understood how mulch would prevent a brief shower from getting to her plants' roots, and came up with her own working solution. But she also understood the benefits of using mulch.