Watering Big Trees

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Need help with how to water big trees?

Many folks ask how to water big trees. So that means gardeners are wondering if they should water mature trees. Further, you may be wondering how much water those old trees actually need. And we’ve got some answers to help you figure out best practices about watering big, mature trees!

Drought does stress out mature trees!

Big, mature trees can really be negatively impacted by lack of water. And lack of water might be caused by drought, insect issues, climate change, or other factors. But whatever the cause, if your big, old tree needs water, getting it to them the right way can help them survive.

Slow, deep, repetitive watering under the cedars may help them through the summer. Just try not to soak the trunk of the tree while you’re at it.

Old native trees may also need watering!

For years horticulturists and arborists in the Pacific Northwest have been coming to terms with the idea that we’re going to eventually lose many of our native trees. And this loss is likely due to climate change and related issues. In truth, these issues mean these trees may need more water than they’re getting from rainfall.

Sadly, one of the first species we expect to go is our beautiful western red cedar or Thuja plicata. And other natives will probably follow this beauty’s lead.

Consider how development may cause a big old tree to need watering…

Recently, we hired New Leaf Arboriculture to help us with some of our biggest tree concerns. And one old tree we were worried about is an enormous, multi-leader western red cedar.

This gorgeous tree has lived through quite a bit of change, particularly in the last few decades. At some point in its long history, a road was paved within feet of it. Later, as recently, as the 1980s it was one among many trees in an undeveloped forested wetland. And kids had nailed a tree house to it during the 1960s and 1970s.

Then, in the 1980s, much of land was cleared around it. And eventually a large building was constructed adjacent to it. Then, because runoff had become an issue from the paved road, much of the water that it (and its remaining neighbors) relied upon was rerouted into a county ditch.

Moreover, the ground above its uptake roots was carpeted with landscape fabric and water-diverting beauty bark.

It’s no wonder this tree was struggling! Rainwater and soil moisture it was relying on was no longer available to this big tree. So, it had begun to suffer. And that means watering this big mature tree by a gardener was it’s last, best hope!

Sparse green growth on the tops of these cedars indicates stress.

Eric and Vance of New Leaf cleaned up much of the dead inside of this beauty and added safety cabling just in case it starts failing in wind or because of its many stresses. And, they reminded me:

“Get some water on this tree!”

After our arborists assessed this tree, they insisted we start watering this tree. But the question of how to water a mature tree was still there. And the question of how much water to give the tree was also in front of us.

How deeply do mature tree roots need to be watered?

Tree feeder roots only go several inches into the earth. But it takes a while to get a good amount of moisture into already dry soil. And if those roots are burdened by fabric and wicking bark, it’s an even bigger challenge.

So if you can, get rid of that bark layer and the fabric before you start watering.

However, by watering slowly and deeply and repetitively over the course of several days and weeks, mature trees can get watered.

Should I use a sprinkler or soaker hose?

Figuring out what kind of tool to use to water your big trees might be challenging. So consider these options for watering big trees:

• Soaker hoses can be helpful, but you may want to hand saturate the soil before you rely on them. That’s because soaker hoses may drip so slowly it takes forever to get really tough, dry soil wet the first time. But, if you have semi-moist soil in place before using the soaker hoses, they may help keep up the moisture levels over time if you run them consistently and often.
• Apply mulch over soaker hoses. Putting mulch over the soaker hoses can help keep the moisture from the hoses from running off. And it will slowly release downward to your thirsty big tree roots.
• Sprinklers are okay, but not the best. That’s because a lot of the water from overhead sprinklers simply evaporates in the air before it gets to the soil surface to water your mature tree roots.
• Don’t spray the tree trunk when you water big trees. Same rules apply for smaller trees too. That’s because too much moisture building up at the point where the tree enters the earth can lead to rot.

Could it be that your mature tree does not need watering?

Big mature trees often do not need to be watered. In fact, over time, they grow adaptations that should help them through normal dry cycles. And sometimes the yellowing you see on an older tree isn’t a problem. Instead, it may be natural behavior.

So how can you tell if your tree needs watering or if the dying parts are a problem?

Things to consider before investing in all that water:

• What part of the tree is yellowing and dying back? If the tips are dying, you may need to water.
• If the interior of the tree is yellowing, it may not need watering. That’s because trees (including evergreens) naturally shed some older leaves. And these tend to be away from the tips of tree branches.
• Are you seeing dieback or are you seeing something else? Sometimes tree cones add yellow color to a tree. And sometimes the new growth on a tree can be a brighter or “off” color from the typical deep green. If this is what’s happening, you may not need to water.
• Are you seeing a whole lot of cones forming?  Heavy cone set can indicate that the tree is really stressed out. Cones = seeds, and a tree putting out a lot of seeds may be trying to replicate itself that way as a last ditch survival effort. So if you’re seeing a lot of cones, you may want to water your big, mature tree!

Heavy cone set like this on a Thuja plicata can indicate the tree is extra stressed out.

A final note on watering mature trees…

• In conclusion, if your soil is dry: water your big trees.
• Too, if the tops of your trees are sparse: watering your old tree may help.
• Moreover, if your big trees have heavy cone set, hurry up and get some water into those roots.
• As well, if your big trees are more yellow or brown than green, start saturating that root zone.
• Finally, if in doubt, bring in an arborist for help evaluating your situation. They should be able to help you set a course of action toward preserving your precious trees (and costly investment) before it’s too late.