North Texas farmer explains the imperfect science of watering crops

Every year by late spring, my garden and field crops look so healthy and photogenic, they could be seed catalog models. By the end of summer, I steer guests away from my garden, so they don't see how brown and dead my crops are. The cause of my late-season embarrassment is simple: I've yet to master the art of watering.

When I was a child and under the impression that there was some sort of natural way to garden, I relied on seasonal rainfall. If plants wilted, I'd give in and water them with tap water. But I was sure there was some secret to making it through the summer without piped-in water: more mulch, more compost in the soil, shade from a tree.

What I didn't know at the time – and I must admit only occurred to me recently – is that there's nothing natural about farming. Except for blackberries and maybe prickly pear, I can think of no food crops we grow in Texas that haven't been imported from some other part of the earth and planted in soil removed from their native habitat.

Most of what we find suitable for food has come from Asia, Africa and Central and South America – areas where it rains monthly, weekly, maybe even daily. That means we have to water them frequently. The Texas climate with its record-breaking drought just doesn't cut it.

So, I've accepted the fact that I need to water my crops, and that's about all that I know. How much to water is a guess – one I make with vague notions and a little experience. If not for the resilience of most food crops and their ability to accept a wide range of less-than-ideal conditions, I'd be a failed farmer.

I work among my crops daily, and foremost in my mind is determining what needs to be watered. I consider several factors in my evaluation.

When was the last rain?
No matter what time of the year it is, if we get three inches of rainfall of a Sunday, we will likely not need to water any crop until the end of the week. I have a rain gauge near my garden to keep track of rainfall, and I'm able to make better decisions from its measurements than from what's reported in the news, based on precipitation at DFW Airport an hour away from my garden.

How does the soil look?
The heavy clay soil of our region is darker when it's moist and lighter when it's dry. A dark gray to black soil tends to have sufficient moisture; a light gray soil is usually dry. Where soils are sandy, moist soil will look darker and more vivid in color. Dry soil will look lighter, less vivid — it's like the difference in wet or dry blue jeans. Dry, prairie soils will also crack open when they're too dry for crops. The drier they get, the larger the cracks will open, until they're large enough for cats to hide in.

How does the soil feel?
If I cannot poke my finger several inches into tilled soil because it's too hard, then it's too dry. The soil should feel moist and cool to the touch just below the surface and down as far as my finger will reach.

Sometimes I'll dig out a little soil from below the surface with my hand. If the golf ball-sized clump has good moisture content, it will be pliable and the soil particles will stick together. If the soil crumbles apart and is gritty and dusty, then it's too dry for crops. If water squeezes out of it like a sponge, it's too wet, which is rare except after a good rain or where lawn irrigation is being overused.

Is the soil in a raised bed or at ground level?
Raised beds tend to need watering more often. Soil at ground level tends to be more connected to the layer of moist soil that our clay soil keeps within reach of plants' roots during spring or after a rain, and therefore may not need watering as often.

Is the plant in a pot or container?
Potted plants require watering almost daily, and sometimes several times a day when the weather is hot. Larger pots retain water longer, but larger plants require water even if they're in large pots.

For plants in pots, the ratio of soil to the size of the plant is the important factor; a plant 12 inches tall in a pot that's the size of cola can will need frequent watering. The same plant in a pot the size of a 5-gallon bucket will require less watering.

What's the weather like?
In 100-degree heat in the middle of summer, it's nearly impossible to overwater. I water everything daily in the summer; it's the only way I've found to keep my crops alive. On the other hand, in spring and fall when the days are shorter and the temperatures are lower, I water less often: once or twice a week maybe.

How do the plants look?
I try to keep my crops tended well enough so that they show no signs of stress. Often, though, I will find a squash plant collapsing in mid afternoon or sections of tomato vines turning crispy brown. These are both signs that I'm underwatering.

In contrast, if plants turn yellow with areas of mushy leaves and stems that turn brown and black, then they're being overwatered.

What size is the plant?
Established tomato vines have longer roots that reach further below the surface of the soil, most likely where there's a more continuous source of moisture. They can survive with less frequent watering.

Seedlings that have just sprouted, on the other hand, may have roots less than half an inch long, barely penetrating the surface of the soil. Tender sprouts will need more attention and more frequent watering, sometimes several showers each day so that the surface of the soil never dries out.

How much water I give each plant, bed or row is inexact. Generally, I pour near the base of each plant a volume of water that I imagine would flood the area underneath the plant to a circumference and depth equal the plant's height and width. Except for vining plants, most plants tend to send down roots like a smaller, inverted copy of what the plant looks like above the ground.

Specific plant needs
Under squash, beans and tomatoes, I envision smaller copies growing upside down and underneath the soil. I pour, sprinkle or drip-irrigate enough water at the place where the plant meets the ground so that the imaginary underground plant is drenched. For a squash plant, for example, that's about a gallon or two of water.

Beans and peas, I've learned, need very little water. Squash, cucumbers and melons are water hogs; in the summer and fall, I water them daily, sometimes twice a day if they wilt often.

Tomato plants should be watered regularly. For mature tomato plants, I find that about five gallons of water every three or four days is sufficient.

Kale, Swiss chard and collard greens and most herbs need enough water in the summer to keep the soil very moist and just short of soggy. In the fall, winter and spring, I dial down my watering and let seasonal rainfall bear the burden. When winters are dry, I drag out the watering can.

Because my drip irrigation system became useless after a late season freeze caused it to burst last spring, I've watered my crops by hand this year — sometimes with a watering can; most often with a hose connected to a rainwater harvesting tank. I try to avoid hitting the leaves with water, especially tomatoes and squash as they are susceptible to fungal diseases if their leaves are wet.

With collard greens, kale and Swiss chard, I intentionally blast the leaves as I water to knock down aphids — these plants rarely suffer from fungal disease. I try to water slowly and patiently, allowing a small trickle of water to penetrate deep below the top of the soil rather than merely wetting the soil's surface and moving on.

Of all the tasks in the garden, watering is the most crucial and hardest to master. Complicating the matter, what works for one farmer in a certain area may not work for another elsewhere.

Despite the resilience of plants and their ability to endure extremes, prolonged exposure to overly dry or soggy soil will eventually take its toll. In a row of more than 60 tomato plants, I recently pulled out five that had died from overwatering even though the rest look great, and they have received the same quantity of water at the same frequency.

Trial and error is the best way to learn how to water. That I can keep some of my crops alive for as long as they can possibly bear fruit is not so much a testament to my mastery of watering as it is to the huge number of mistakes I've made — and learned from.

Marshall Hinsley waters a bed of basil in his garden.

Photo by Marshall Hinsley

Marshall Hinsley waters a bed of basil in his garden.