Here’s something we see every spring as ISA-certified arborists in Lincolnshire: more trees are damaged by too much water than too little.
If you have a sprinkler system, there’s a good chance it’s quietly stressing your trees — even while your lawn looks great.
Water at 7–9 AM. Not midday. Not at night.
Morning is the only time that makes real sense.
The soil absorbs what it needs, and the surface dries naturally through the day. No wasted water, no moisture sitting on bark overnight.
Midday — most of the water evaporates before it reaches the roots.
You’re paying for water your trees never receive.
After 7 PM — moisture sits on bark and soil all night with no sun to dry it. That’s how fungal problems start. Damping off, fungal spots, rust, rhizosphaera needle cast, leafspot, powdery mildew — we diagnose these in Lincolnshire trees every season, and evening watering is almost always part of the story.
If you missed the morning, 5–6 PM works — there’s still enough light and warmth for things to dry before dark.
Your sprinkler system is built for your lawn, not your trees
This is the conversation we have with homeowners more than almost any other.
Lawn grass needs frequent, short watering cycles. Trees need deep, infrequent soaks. When your irrigation system runs the same schedule for both, your trees are getting hit at the base three or four times a week — far more than they need.
Watch especially for water spraying onto plant material. Sprinkler systems spraying arborvitae and spruce directly is one of the most common causes of needle cast and fungal decline we see in this area.
Rust and Rhizosphaera needle cast in particular are largely irrigation-driven diseases — and they almost always trace back to heads that were never adjusted as the trees grew.
Signs your irrigation is harming your trees:
Yellowing leaves despite the tree looking otherwise healthy Soil around the base that never fully dries out Moss or algae on the bark near ground level White mushrooms appearing at the base in a pattern around the root zone — this is where root rot lives. By the time you’re seeing mushrooms, the damage is already underway, and the cause is almost always water that had nowhere to go Leaves wilting even though the soil is wet — this is mushy roots from root rot, not drought.
Older systems — a common problem in our suburbs
Many homes here have irrigation systems that are 15–30 years old. The heads were aimed at open lawn when they were installed. Since then, your trees have grown — but the heads haven’t moved.
Five things to check right now:
-Run every zone and watch it. Walk the yard while the system runs. Look for heads with water spraying onto plant material, stuck rotary heads, and pooling water that isn’t absorbing.
-Redirect heads near trees. Most heads can be adjusted without replacing them. Keep water on the lawn, away from trunk bases and foliage.
-Separate your schedule if you can. Trees once a week, deeply. Lawn two to three times a week, shorter. If your system can’t run separate zones — favor less frequent for everything.
-Check your run times. Illinois spring lawns typically need 20–30 minutes, once or twice a week. If your system is running daily from a schedule that was never updated — that’s too much.
-Add a rain sensor. Older systems often don’t have one, or it’s failed and bypassed. A basic sensor costs under $30 and stops your system from running the morning after it rained.
Do’s and Don’ts: Watering Trees the Right Way
| Water deeply and infrequently — once a week at the drip line, not the trunk. Let the soil dry between waterings. Soil should be firm to the touch, not muddy or spongy. Firm, moist soil that dries between waterings is what a healthy root zone feels like. If it’s muddy, you’re already overwatering. | Don’t water at night. Moisture sitting on bark and soil with no sun to dry it creates the exact conditions for damping off, fungal spots, rust, Rhizosphaera needle cast, leafspot, and powdery mildew. Improper irrigation causes the biggest issues we see in landscaping — more than drought, more than pests, more than almost anything else. It’s behind more tree problems in this area than most homeowners realize. |
| Water in the morning between 7–9 AM. This gives roots time to absorb moisture and allows the surface to dry naturally before evening. | Don’t ignore mushrooms at the base of a tree. White mushrooms growing in a pattern around the root zone are a sign of mushy roots and active decay below the surface. By the time you’re seeing them, the damage is already underway. |
| Check your sprinkler zones individually. Walk the yard while the system runs and watch for heads directing water spraying onto plant material — arborvitae, spruce, and other evergreens are especially vulnerable. | Don’t wait if a tree looks distressed. A tree showing wilting, yellowing, or browning leaves despite wet soil isn’t struggling — it is already damaged. The window to intervene is shorter than most people expect. |
| Separate your irrigation schedule. Trees need water once a week, deep and slow. Lawn needs two to three shorter cycles. These should not be the same schedule. | Don’t let heads spray trunk bases or plant material. Keep water on the lawn where it belongs. |
| Install a rain sensor if you don’t have one — or verify your existing one is actually working. | Don’t mistake wet soil for healthy soil. Soil that’s consistently muddy is suffocating roots, not feeding them. |
We’re not an irrigation company and don’t service irrigation systems — but as ISA-certified arborists, we can walk your property, assess what your trees are showing us, and give you clear recommendations on what your watering schedule is doing to them. Sometimes that conversation alone saves a tree.
When do trees actually need water?
Established trees — in the ground three or more years — are more drought-tolerant than most people realize. In a normal Illinois spring, they need very little help.
Water when: no significant rain for two or more weeks, leaves are curling or browning at the edges, or the tree was planted in the last 1–2 years.
Stop when: the soil 2–3 inches down is already moist, rain is coming in the next day or two, or you’re seeing any of the overwatering signs above.
When you do water — water at the drip line, not the trunk. Deep and slow, once a week. Not a little every day.
Our ISA-certified arborists assess tree health and catch issues early.
Advanced Tree Care — Cook & Lake County Free estimates: 847-587-8500
