Here we go again.

The wet, cool spring that boosted optimism that the drought was over has given way to a hot, dry end of summer that is leaving trees, lawns and plants in dire need of watering.

"The rain we had in the spring doesn't count now," said Kent Honl, master arborist at Rainbow Treecare. "I'm seeing a lot of trees with yellowing leaves. They're shedding their foliage to conserve moisture."

The drought that we thought had ended is now officially back.

The first six months of the year were among the wettest in the 119 years Minnesotans have been keeping such records. By the end of June, only a couple of areas in the northwestern part of the state were still reporting dry conditions, and in mid-July, the U.S. Climate Prediction Center issued a rosy projection that the entire state would be drought-free by Halloween.

But that prediction turned out to be more trick than treat. The weather tables have turned, combining a late-season heat wave with rainfall that's been about 3 inches below normal since July 1. The U.S. Drought Monitor report released last week classified 53 percent of the state — including the Twin Cities — as being in moderate drought and another 26 percent as overly dry.

A stressed maple tree in St. Paul began shedding its leaves in August.

The bottom line: Keep those hoses handy.

Don't let the calendar fool you. There's a commonly held belief that once the prime growing season is over, we don't have to worry about tending to our plants until next spring. That's completely false, said garden writer Deb Brown. In fact, the opposite is true: If you want the plants to still be around next spring, you'd better tend to them now.

"If a plant is drought-stressed, it's much harder for it to survive the winter," she said. "Perennials need to be watered right up until the soil begins to freeze. The same for bushes and trees. I can't think of anything that doesn't benefit from a good soaking once a week. It's really critical that they don't go into winter stressed."

Don't forget the lawn. Yes, you could allow it to go dormant and it might come back in the spring — the emphasis being on "might."

"We had a really bad drought back in the '80s, and experts were telling people to let their lawns go brown and they would come back the next year," Brown recalled. "Well, a lot of them didn't. It depends on the individual lawn, but I wouldn't risk it."

The one-inch rule

As a general rule of thumb, experts recommend one inch of water a week. But that advice comes with a caveat: Lots of factors, including the sand and clay contents of the soil, affect the amount of water that's needed.

"You should get to know your own location," Honl said. "A big part of having a green thumb is knowing the local conditions and how plants react to them."

For instance, in sandy soils, the water will drain away faster. Instead of one major watering a week, you might want to consider two or three smaller ones. And ground that's heavy with clay will hold too much water.

"You don't want to drown the plants, either," he said. "There's a Goldilocks factor here — not too little but not too much."

The best way to determine when you've reached the one-inch mark is to put a container — an empty tuna can is one of the experts' favorites — in the area and then time how long the sprinkler has to run to fill it with an inch of water.

"People will say, 'I have an irrigation system that runs for 20 minutes every other day,' but that doesn't mean anything," Honl said. "Irrigation systems are different, and the [water volume] settings are different."

While people remember to tend to young trees, it's just as important to water mature trees during drought conditions, he said.

"A tree is a huge water-pumping system," he said. It absorbs water through its root system — which tends to be the same size as the its crown — and sends it to the leaves, where it's released into the air via evaporation. "On a hot, windy day, a tree can go through hundreds of gallons of water," he said.

Many people like to put a fall application of fertilizer on their lawns, which will help it grow in thicker in the spring, preventing weeds. But reconsider it this year if your lawn is stressed, Brown said.

"If the lawn is healthy, it definitely pays benefits," she said. "But if it's dry and crispy, don't do it."

The experts also agree on the need to monitor the weather and adjust accordingly — always good advice but particularly relevant this year.

"This has been such a bizarre summer that I don't know what to expect next," Brown said.

Jeff Strickler • 612-673-7392