From the Denver Office of the City Forester
If water is life, then mulch is a lifesaver! When we talk about tree care in the summertime, we
are mostly talking about the one-two punch of watering and mulching. Below you’ll find a roundup of some simple tips for summertime tree care.
Before you start watering, make a plan based on the trees you have. Answering these questions
can help you make a watering plan that works.
- How old are your trees?
- How much water will they need?
- How do you tell if you’ve watered enough?
- When should you water?
- When should you not?
How can I check if my tree needs to be watered?
Easy! Feel it with your hand. Dig down into the soil a few inches and squeeze with your hand to
feel if it is wet, dry or somewhere in-between.
How much water do I use?
If your tree is young and still establishing, it will need a little more TLC, so shoot for 15-20
gallons, every 2-3 days. After your tree becomes established (it usually takes a two-inch caliper
tree 2-3 years to establish), you can reduce the watering frequency. However, we still
recommend following the 10 gallons of water per inch caliper of the tree, watering when we
experience long periods without precipitation and throughout the winter. Allow soil to dry
between watering’s and continue to monitor your soil moisture to determine when your tree
needs to be watered.
How can I make sure water reaches deeper into the soil?
A simple hose is the most basic tool needed to water your tree, but soaker hoses, soft spray
nozzles and soil needles can help break through the soil surface. Most absorbing tree roots are
found in the first 12-inches of soil depth; apply water slowly so it has time to absorb into the soil
and reach these vital roots.
How can I tell how much water my tree is getting through my hose or irrigation system?
You can determine your hose’s output by taking a container of known quantity, like a gallon jug
or five-gallon bucket, and setting a timer for how long it takes the hose to fill up the container at
a trickle. Then you can calculate how long you should trickle your hose to achieve a certain
quantity of watering. Irrigation systems themselves generally do not provide enough water for
young trees during their establishment phase, so plan on giving supplemental water as well and
checking the soil moisture regularly.
As travel begins to pick back up and Denver residents start hitting the road, don’t forget to make
a tree care plan while you’re gone. When possible, ask a neighbor, family member or friend if
they’ll water for you and you can offer to do the same for them. And remember to check with
your utility department for preferred times, right-day usage and other potential temporary
Mulch: it does so much! Keeping a mulch ring around young trees keeps them safe from mower
and string trimmer damage, which can be an easy point of entry for pests and disease. It also
holds moisture in and protects against temperature extremes. It decomposes and adds nutrients
to the soil, too!
Here’s how it’s done:
Apply wood chips, bark, or other organic mulch 2 to 4 inches deep in a ring around the base of
the tree, but at least 3 inches away from its trunk. Mulch reduces soil evaporation, improves
water absorption, insulates against temperature extremes and can break down over time,
adding necessary nutrients to the soil. Make sure to replenish your mulch as necessary, at least
a few times a year.
We said MULCH, not rocks or grass.
Rocks as “mulch” are bad for trees. They retain heat, causing the soil temperature to rise and
that increases evaporation. Plus, rocks don’t provide essential nutrients and can actually
change the soil chemistry, which can be unfavorable for many trees. They’re not all bad, though
– rocks and xeriscape lawns can be a way to conserve water in other areas of your garden, but
it is essential that the area with your tree roots is covered with mulch or other organic material.
For different reasons, grass around the base of the trunk is also not recommended. Why?
Because grass is greedy. It competes with young trees for moisture and nutrients in an already
water-scarce climate. Plus, having grass close to your tree increases the risk of mechanical
damage to the trunk from lawn mowers or string trimmers.
For those of you ready to graduate from Mulch 101 and really dig into the topic, we present
vertical mulching. Vertical mulching can alleviate soil compaction, which jeopardizes tree health
and is commonly found in Denver in areas with clay soil or recent construction. Vertical
mulching improves soil conditions and allows for deeper water penetration. Yep – it’s all related.
It’s accomplished by removing columns of poor-quality soil around the tree in a radial or grid
pattern, and then filling those columns with compost.