> I’ve been an arborist for 35 years and it is my opinion that it is healthier for trees to be planted outside the lawn area.

Kill your lawn. Lawns don't belong in Colorado. Get your city to adopt rainwater harvesting measures, use it to create microclimates with native flora. That'll make it easier for you to grow trees, and better use of rainwater will reduce/eliminate the city's need to upkeep with water.

Brad Lancaster has a website with this and other ecosystem-minded permaculture techniques. He's in AZ but the techniques are adaptable to CO. https://www.harvestingrainwater.com/water-harvesting/