Debbie Arrington

Don’t boil tomatoes alive! Why not to water when it’s hottest

Blossom end rot is a common problem on tomatoes, especially during high heat.
Blossom end rot is a common problem on tomatoes, especially during high heat. TNS

This tomato plant was a goner. Thinking I was helping, I only hastened its rapid demise.

How? I watered in the late afternoon. It was a hard lesson on “proper irrigation.”

During our recent triple-digit heat wave, this particular tomato vine wilted badly. On an after-work visit to my community garden plot, I was alarmed by this plant’s near-death appearance. Its leaves brown and curling, this little tomato looked like it had been under a heat lamp all day. I immediately grabbed a hose.

I thought a deep soaking might revive this bush and save its baby tomatoes. I was wrong.

“In extreme heat, you don’t want to give a plant water, even if it’s wilted,” explained plant expert Kate Karam of Monrovia Nurseries. “The plant needs a chance to recover first and for the soil to cool down.

“When temperatures reach over 100, water late at night or early in the morning,” she added. “Don’t water in the late afternoon or you’ll boil your plants’ roots alive. They’ll literally steam; the soil is just too hot.”

That’s what happened to this sad tomato. The next morning, instead of bouncing back into a green and happy bush, it drooped into a heap of crispy leaves. So much for this plant. Fortunately, its neighboring tomato vines came through the heat spell OK. This summer’s harvest will not be a total loss.

This tomato death was a reminder of how many things can grow wrong in the summer garden.

“It’s just been the oddest year and not really predictable,” said Karam, who gives advice to gardeners nationwide. “This year has been really interesting for people who have gardened in California for a long time. The last 10 years – sure, we’ve had drought – but gardening overall has been pretty predictable. This year, everything is so different.”

Take our June weather, for example. This is that crucial time when baby tomato plants do a lot of growing and begin to set fruit. They prefer a gradual climb in temperature, slowly warming up as their vines grow and first fruit ripens. But in Sacramento this June, highs ranged from 71 to 108.

Tomatoes love warmth but only tolerate high heat. That rapid rise in temperatures causes them to shut down fruit production and concentrate on survival. They drop blossoms or refuse to set new tomatoes. They develop brown spots on tomatoes that are forming (signs of dreaded blossom end rot).

To help your tomatoes make it through this summer, treat them like you’d treat yourself. Keep their roots hydrated (but not soggy) and cool. Add a layer of straw mulch or other organic material to maintain that steady soil moisture and temperature.

If triple-digit heat is predicted, even sun-loving tomatoes need some relief. Erect an umbrella to shade the vines in late afternoon or place some burlap over their tomato cages. That will not only cool the vines, but prevent sunburned fruit.

And never water in the late afternoon.

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