Autumn Blaze maple in Colorado: why it struggles, and what to plant instead

Why Autumn Blaze struggles here

Autumn Blaze is a Freeman maple (Acer x freemanii 'Jeffersred'), a cross between red maple and silver maple. It sells because it grows fast and turns a big, reliable red in fall. The catch is underground.

Our soil locks up its iron

Most Front Range soil is alkaline. CSU Extension explains that above pH 7.0, iron in the soil gets chemically tied up in forms roots cannot absorb, even when there is plenty of it. Red maple, one of Autumn Blaze's parents, is on CSU's list of trees highly susceptible to the result, iron chlorosis: leaves go yellow between green veins, growth stalls, and a tree that stays chlorotic year after year slowly declines. Overwatering and compacted soil make it worse.

What the 2024 list says

The 2024 Front Range Tree Recommendation List rates the whole Freeman group, Autumn Blaze included, Not Recommended, with the note "Develops chlorosis in alkaline soils." It flags soil chemistry as the critical problem, and also cautions that Freeman maples throw up suckers and reseed. More on the Autumn Blaze plant page.

Treatment works, then wears off

You can green up a chlorotic maple, but per CSU, iron chelates in the soil last anywhere from less than a season to about two years, and iron sulfate plus sulfur up to three or four years. So it is a standing appointment, not a fix. CSU's own advice for high-pH soils is to pick a tree that tolerates them in the first place.

Banned from the street strip

If the tree is going in the strip between sidewalk and street in Denver, the question is settled for you. The City Forester's Street Tree Planting Guide says: "Per OCF Rules and Regulations, the following trees may not be planted in the public right-of-way due to safety concerns, pest/disease concerns, and/or invasiveness," and the list includes "Acer x freemanii (all cultivars), including Autumn Blaze maple." (Denver Street Tree Planting Guide.) Planting any street tree there also needs a free permit from the City Forester. Other cities set their own rules, so check yours.

When an Autumn Blaze can be fine

Chlorosis is about the dirt under the tree, not a curse on the cultivar. CSU PlantTalk puts it as Autumn Blaze "does suffer some from iron chlorosis," and CSU ties the problem to high pH, soggy soil and compaction. So an Autumn Blaze in soil that tests closer to neutral, drains well and is not overwatered can stay green.

• Thinking of planting one anyway? Get a soil test first. If the pH comes back high, which is the usual result here, put the money toward one of the trees below.
• Already have one that is yellowing? It is not an emergency. Ease off the water if the soil stays wet, keep mowers and foot traffic off the root zone, and budget for repeat iron treatments if you want to keep it green. Why is my tree dying in Colorado helps rule out other causes.

Better trees to buy instead, ranked

Ranked by how close each comes to what Autumn Blaze promises (big shade, fall color, speed). All seven are rated for the Front Range on the 2024 list, none is flagged there for soil chemistry, and all appear on Denver's Approved Street Tree List, as the species or a named cultivar. Five different genera, too, so your block does not end up with one tree on repeat.

One caveat: CSU names whole groups like maple, elm and linden as prone to chlorosis, so no tree is immune if the soil is soggy or compacted. The 2024 list judges species by species, which is why these made the cut and Autumn Blaze did not.

• 1. Shumard oak Quercus shumardiiRecommended for Most Sites · 40 to 60 ft tall · moderate growth · low to medium waterThe closest swap for what the Autumn Blaze tag promises: a big shade tree that turns red in fall, with no concerns flagged on the 2024 list. Its one note is to buy from a northern seed source, so ask the nursery where it was grown.
• 2. Kentucky coffeetree Gymnocladus dioicusRecommended · 60 to 75 ft tall · moderate growth · low to medium waterBig, long-lived, rated high for hail, and nothing flagged on the list. Fall color is yellow rather than red, and female trees drop messy pods, so ask for a seedless cultivar like Espresso.
• 3. Miyabe maple Acer miyabeiRecommended for Most Sites · 30 to 40 ft tall · slow growth · low to medium waterIf it has to be a maple. The list does not flag it for soil chemistry the way it flags Autumn Blaze, and it colors orange, red and yellow. It is smaller and slower, hardiness varies by source, and it sulks after transplanting, so start with smaller stock.
• 4. ACCOLADE elm Ulmus davidiana var. japonicaRecommended · 50 to 60 ft tall · fast growth · low to medium waterThe pick for speed, which is the other thing people buy Autumn Blaze for. The list notes it resists elm leaf beetle and does not get scale. Fall color is yellow.
• 5. American linden Tilia americanaRecommended · 50 to 75 ft tall · moderate growth · medium waterDense summer shade and early-summer flowers that pollinators work hard. It wants steadier water than the others, and leaf edges brown in hot, dry wind, so give it a sheltered spot.
• 6. Bur oak Quercus macrocarpaRecommended · 60 to 80 ft tall · slow growth · low to medium waterThe long game. Bur oak takes clay, low water and high wind, and lives for generations. It is slow, so buy the biggest one you can afford.
• 7. Bigtooth maple Acer grandidentatumRecommended · 20 to 30 ft tall · slow growth · low to medium waterA native maple with the red-orange fall color, flagged for nothing on the list. It is a small, slow tree and stocked less often, so it suits a smaller yard and a buyer willing to call around.