Authored by:
Mauricio Avila
Dry Augusts will test what you’ve been working toward all season – and you’ll feel it in your roots.
By August, most gardeners are well acquainted with heat. But full-on drought does something more complex and lasting to the soil than heat alone. Understanding how soil holds and loses water, and what happens when that water disappears, can help you make smarter decisions during the dry weeks that define late summer in much of the country.
What we’ll tackle:
After a good rain, soil gets saturated. Every pore fills up. Then gravity does its work, pulling the excess water that the pores can’t hold against gravity down through the soil and away. What remains after that drainage is called field capacity: the maximum amount of water that soil can hold against gravity. This is the starting point for thinking about drought.
From field capacity, water leaves the soil in two ways. Plants transpire – they pull water up through their roots and release it through their leaves as part of photosynthesis. And the soil surface evaporates water directly into the air. Together, these two processes are called evapotranspiration, and the balance between evapotranspiration and rainfall is one of the most important factors in determining how drought affects your garden.
Here is where geography matters. In the Midwest, annual rainfall exceeds evapotranspiration, meaning more water falls than evaporates. This excess water seeps through the soil and flushes salts down into the groundwater, keeping the soil relatively clean. Drought there means plants are stressed, but the soil itself tends to recover well.
In the Southwest, the situation is reversed. Evapotranspiration consistently outpaces rainfall. Over years and decades, this means water moves upward through the soil by capillary action. It carries dissolved salts with it until the water evaporates, leaving the salts at the surface of the soil. This is why soils in arid regions tend to have high salinity and high pH – problems that simply don’t exist in wetter climates.
If you live in a dry region and rely on irrigation, be aware that groundwater in those areas often carries significant quantities of dissolved salts too. Every time you water, you’re leaving a small deposit behind. Over several seasons, that can add up, especially if you can’t irrigate enough to flush excess water deep into the soil and take the salts with it.
Think about what happens when you pour salt on a slug. The water is drawn out of the slug’s body by osmosis, and the slug shrivels. The same principle applies to plant roots in saline soil. When there is too much salt in the soil solution, the roots can’t pull water in. Instead, water may actually move out of the roots. The plant experiences drought stress even if the soil contains moisture because the salt makes that water inaccessible. The salts hold on to the water more tightly than the roots can absorb it.
Signs of salt damage look different from simple drought stress. With pure water deficiency, you’ll see wilting and eventual leaf curl. With salinity, the leaf edges tend to show brown scorch marks, working their way inward from the margins. This can be mistaken for fertilizer burn or even a fungal disease, but the pattern – edge burning all the way around the leaf – is distinctive.
Even without salinity concerns, drought creates a challenging dynamic near the soil surface. When the top five to ten centimeters dry out, they dry out fast – much faster than deeper layers. Once that surface layer is dry, further water loss by evaporation slows considerably. But here’s the problem: That’s exactly where the highest concentration of roots is. Plants draw heavily on water from the top few inches of soil, so even a relatively shallow drought can cause significant stress.
This is one reason why daily light watering is often counterproductive. Wetting only the surface encourages shallow roots and loses a disproportionate amount of water to evaporation before plants can use it. A deeper, less frequent watering – roughly half an inch of water per day, or about three inches per week during peak drought – encourages roots to follow the moisture downward and makes much better use of your water.
Watch for wilting as your early warning system. The moment your plants show early signs of wilting – especially in the morning, before the heat of the day – they need a good watering as soon as possible. Don’t wait for severe stress, which can cause lasting damage to root systems.
Consider shade as part of your drought strategy, not just your heat strategy. High temperatures and drought almost always arrive together, and a bit of shade cloth or well-placed tall plants can dramatically reduce how much water your crops transpire. Reducing water demand is just as effective as increasing supply.
Mulch remains one of the best tools you have. A layer of mulch on the soil surface breaks the direct connection between hot, dry air and the soil, slowing evaporation significantly. Just remember to fertilize beneath the mulch, not on top of it, so your amendments reach the soil rather than getting locked up in the mulch’s high-carbon matrix.
If you are in a region prone to salinity – the Southwest, or anywhere that relies heavily on irrigation – adding organic matter and gypsum to your soil can help. Earth Science Fast Acting Gypsum in particular helps repair salt-damaged soils, improving soil structure and creating a more hospitable environment, even under dry conditions. Earth Science Fast Acting Sulfur starts working right away to acidify the soil, but lowering soil pH is a gradual process. That’s why fall is the ideal time to apply it, giving the sulfur time to neutralize soil alkalinity before spring. Remember, low pH means the soil is acidic, while high pH means it’s alkaline.
August drought is a test of how well you’ve been building your soil all season and in previous years. Soils with good organic matter content hold more water, support healthier root systems, and buffer against salinity far better than depleted soils. Combined with slow, deep irrigation throughout the season, healthy soils encourage deeper root growth that helps plants better withstand drought stress. This month’s challenge is also an argument for the investments you’ll want to make come September.
