Zone 13 Summering with Clay Soil
‘The garden suggests there might be a place where we can meet nature halfway.’
— Michael Pollan
A universal truth in gardening is that there is always a season of dread. Everything is lush and gorgeous when the weather is generous. But eventually it’s time to pass through the valley of the shadow of death, knowing not how your garden will fare this year. In my part of the world, that season is summer.
There are three kinds of weather where I garden in the humid coastal tropics: dry and mild, wet and warm, and hot as hell. Winters are a dream. Monsoons are more deluge than drizzle, and cyclonic to boot. Summers are extreme. Salt is in the air, in the ground, in the water. According to the widely followed USDA hardiness zones classification, my garden grows in Zone 13 which basically means there is never any frost as temperatures never dip below fifteen degree celsius.
In peak summer at midday, the air sizzles from heatwave after heatwave, crisping out most of the green and stripping trees to stark woody skeletons. The blinding light bleaches out everything and rippling mirages appear above hot asphalt. Adding more water ‘to cool things down’ is a double-edged sword as humidity levels soar and evaporative cooling stalls.
To compound matters, the soil is clay. Summer sun bakes it into indurate, concrete-like clods. In drought, it shrinks and cracks into platey polygons, crusty with salt and dry as a bone. If you till clay soil, you risk creating hardpan - an impermeable layer that sits below the tilled soil and makes drainage impossible during the next rainy season. When the rain comes, it swells the topsoil and damages it with impact and runoff. Even walking on wet clay soil can lead to smearing and compaction that squeezes air pockets out.
But nothing is all bad. Clay soil, for all its setbacks, is fertile. Clay has a high CEC (cation exchange capacity) meaning clay soil has a negative charge, plant nutrients carry a positive charge and these electrical charges bind them together so nutrients don’t wash off easily like they do in sandy soils. Ironically in summer, clay holds moisture better under its parched exterior making water available to plants even in harsh conditions, provided there is no hardpan preventing the roots from reaching that far down.
Ideas that come from much cooler climes, like Charles Dowding’s no-dig philosophy are still incredibly useful here at the opposite end of the spectrum. Clay benefits massively from cover cropping, mulching and the addition of organic matter. Clay covered in a couple inches of compost and mulch is much more resilient and arable in summer than bare soil exposed to the elements. Cover cropping plays many roles: fixing nitrogen in degraded soil, providing ground cover, and bio-tilling by developing deep tap root systems that leave channels for air, water and other soil life when the plants are cut down. If treated right, clay can transform from being a gardener’s nightmare into a stable, reliable growing medium.
Other general tips for fellow gardeners with harsh summers: shade is your friend. Drought-resistant trees like moringa make great border plantings, letting in dappled sun through their feathery foliage. Shade nets of at least fifty percent can prolong growing time in summer if you can make rudimentary structures to prop them over.
Pick the right crops for harsh summers. Drought-resistant native varieties tend to thrive better under extreme conditions and need less care. Water when the sun is low and keep sensitive plants in containers that can be moved out of direct light during the day. With these practices, a garden will eventually adapt to the hottest summers and require fewer inputs over time. A win.