How to keep 'lawn trees' healthy -- without the lawn

In suburban neighborhoods, most trees live in lawns. What happens when that lawn goes away?

Used to watering on a turf schedule, those former “lawn trees” tend to struggle.

But by understanding their needs, mature trees can thrive in their new surroundings.

“Trees actually do better when you take the lawn out, but you have to do it carefully,” says Joanna Solins, UCCE Environmental Horticulture Advisor for Sacramento, Solano and Yolo counties.

Trees don’t like change; they literally grow accustomed to their surroundings, above and below ground. That includes irrigation; lawn trees get lots of water in shallow twice-weekly doses.

As California continues to move away from nonfunctional turf (NFT) or ornamental lawns, more trees are at risk.

“Overall, we’re losing our tree canopy – that’s not a good thing,” Solins explains.

There are several factors, from drought to disease, she notes. “If they’re not watered, there’s a real huge impact.”

Value your mature trees

Mature trees are the most valuable plants in any landscape – for you and your community. Trees create shade, provide habitat, reduce air temperature, clean the air and sequester carbon.

Remember: They took a lot of time to get that big.

“Tree planting is wonderful, but it takes decades to replace a big canopy tree,” Solins says. “You can’t do it in your lifetime. It’s much easier to save trees than replace.”

Trees at highest risk during lawn conversions are species that need the most water such as coastal redwoods. Signs of distress include browned needles and limb drop.

“Trees take a long time to show distress, sometimes years,” Solins notes.

Understand roots

With or without lawn, tree care starts at the roots.

“In general, trees should be given deeper, less frequent watering than lawn,” Solins says.

Deeper watering encourages trees to grow deeper roots, but how deep? “Most of a tree’s fine roots that take up water and nutrients are in the top 12 to 18 inches of soil,” she says. “That’s not particularly deep.”

Those fragile feeder roots go all around the tree and extend past the tree’s canopy, the furthest reach of its branches. When irrigating, keep that in mind.

“If you’re putting in drip (irrigation), make sure it goes all the way around on the outer edge of the canopy and beyond it,” Solins says. “Those roots often extend far beyond the edge of the canopy.”

Follow that same advice for soaker hoses.

Watering too close to the trunk can cause rot or other issues, she adds. “It’s very common to see a little ring of irrigation right around a tree. It’s not getting water where it needs it. It’s OK for a baby tree, but for mature trees, I would not irrigate within 5 or 10 feet of the trunk.”

Preparing a tree for change

Before taking out the lawn, help your tree in advance. “Hydrate your tree before any disturbance,” Solins instructs. “Give it lots of deep watering. It will make it more resilient during landscape change.”

Avoid soil compaction under the tree’s canopy; those feeder roots need air pockets.

“Minimize disturbance of the root zone as much as possible,” she says. “That extends several feet beyond the tree’s canopy. Never use sod cutters or heavy equipment under the canopy. Damage to the roots can be a real problem.”

After the lawn is removed, phase in the tree’s new watering schedule. Gradually cut back on irrigation from twice weekly or weekly to twice monthly.