Do you need a permit?
No permit required for most private trees
Thornton has a city forester with real teeth, but the power points the other way: the forester can order a tree DOWN, not stop you taking one down. The city's tree article in the municipal code contains no permit, no application and no diameter threshold for a homeowner, and the only landscape permit Thornton issues is a construction permit for new or re-development of a property. Removing a tree in your own yard is not a permitted activity in Thornton.
What's protected in Thornton
- Landscaping installed under an approved development landscape plan, which becomes public record of the required landscaping
- Trees on land going through a Conceptual Site Plan, Major Development Permit or Minor Development Permit
Fees, penalties, and the ordinance
- Fee
- No fee for a homeowner, because no permit exists. The Landscape Construction Permit, which applies to new or re-development, is 1.5 percent of total contract cost with a $30.00 minimum, plus materials sales and use tax of 3.75 percent on 50 percent of contract cost.
- Penalties
- Violating the Trees and Plants article is punishable as provided in § 1-8(a) (§ 46-101). Failure to comply with a notice to correct is itself unlawful, and the city may do the work and lien the property for the cost (§ 46-103(c)).
- Ordinance
- Thornton Code of Ordinances Chapter 46 (Parks and Recreation), Article III — Trees and Plants, Division 2, §§ 46-101 to 46-105 (Code 1975 §§ 63-1 to 63-5; Ord. No. 596, 4-8-74; Ord. No. 2323, 6-13-94; § 46-102 amended by Ord. No. 3724 § 1, 2-12-25). Code codified through Ordinance No. 3760, adopted January 27, 2026.
Worth knowing
- The tree article is about compelling removal, not licensing it. § 46-102: the city forester "shall also have the authority to order the removal of any trees or plants upon public or private property when the city forester determines such action is necessary to prevent the spread of disease or insects, and to protect the public health and safety based upon standards established by the International Society of Arboriculture."
- Same section: "It is declared to be a public nuisance for an owner to maintain a tree or plant in a condition that presents a threat to the public health and safety."
- Division 1 of the Trees and Plants article is literally reserved — §§ 46-76 to 46-100 are blank. Everything operative sits in Division 2, Trimming and Removal, and none of it requires an owner to ask permission.
- A notice to correct gives you up to 30 days (§ 46-103(b)), you can appeal in writing to the city manager's office within seven days (§ 46-104), and in an immediate threat the forester may enter on a court-issued seizure warrant (§ 46-105).
- Thornton's landscape permit is a development instrument. The city describes its Landscape Construction Permit application as being "for landscape and irrigation for new or re-development of a property," and directs "Homeowners with questions about existing landscaping" to contact the City Landscape Architect rather than to apply for anything.
- A landscape mitigation plan under the Development Code is "a plan for the replacement of plant material that is removed, destroyed or otherwise negatively affected by the development of a property" — triggered by development, not by a homeowner removing a yard tree.
- Thornton does not license tree service companies. Chapter 42, Licenses, Permits and Businesses, covers alcohol, circuses and carnivals, massage parlors, entertainment clubs, pawnbrokers, sexually oriented businesses, ice cream vendors, marijuana and mobile food trucks — there is no tree or arborist license, unlike Denver, Aurora, Lakewood, Fort Collins and Pueblo. Check your contractor's insurance yourself.
- Thornton Forestry runs an Emerald Ash Borer information program and an annual Arbor Day tree sale, and publishes Front Range planting and pruning guides.
- Thornton will not referee neighbour tree problems; leaves falling from a neighbour's tree is a private matter.
What we could not confirm
We would rather tell you what we don't know than guess. Call the office below to confirm these before you cut.
- — The exact text of the Development Code landscaping standards at § 18-491 et seq. Chapter 18 is not carried on Municode and is published separately by City Development, so we relied on the city's own description of when a landscape permit is required.
- — Who owns and maintains street trees in Thornton. The municipal code's tree article does not address it.
- — Whether any overlay, floodplain or open space designation adds tree duties to an otherwise ordinary residential lot.