Trees Please at the Pueblo Zoo

Project Overview

Trees Please planted trees at the Pueblo Zoo to help restore the existing tree canopy diminished by storms, drought, pests, disease, and aging. The project had two goals:

  • Restore and diversify the zoo’s tree canopy.
  • Participate in the Colorado Tree Coalition’s (CTC) Trees Across Colorado Program, which provides low-cost trees to Colorado communities and facilitates purchasing trees in air-pruned pots which promote a dense, fibrous root system without girdling.
Air-Pruned Pot

Thirty trees were purchased through the program. The project’s total investment for trees, straps, stakes, flags, and signage was $3,160, including a $2,100 grant from Supporters of Horticultural EDucation (SHED).

Tree Selection and Establishment

Thirteen species were chosen to diversify the zoo’s tree canopy. The sheltered setting and irrigated grounds at the zoo offered an opportunity to test species not previously planted in Pueblo. The tree species shown in green below are new to the Pueblo area and show promise for their drought tolerance, adaptability to Pueblo’s alkaline, poorly drained, and compacted soils, and resistance to pests and diseases. Also, all but eight of the thirty trees came in air-pruned pots, allowing for a comparison of their establishment over time with conventional container-grown trees.

Species Planted

  • State Street Miyabei Maple — Acer miyabei ‘Morton’
  • American Hornbeam — Carpinus caroliniana
  • Northern Catalpa (Catalpa speciosa)
  • American Yellowwood (Cladrastis kentuckea)
  • Autumn Gold Ginkgo (Ginkgo biloba ‘Autumn Gold’)
  • Espresso Kentucky Coffeetree (Gymnocladus dioicus ‘Espresso-JFS’)
  • Tuliptree (Liriodendrum tulipifera)
  • Spring Snow Crabapple (Malus ‘Spring Snow’ sproutfree)
  • English Oak (Quercus robur)
  • Shumard Oak (Quercus schumardii)
  • Swamp White Oak (Quercus bicolor)
  • Princeton Elm (Ulmus americana ‘Princeton’)
  • Allee Elm (Ulmus parvifolia ‘Emer II’)

Earth Day Planting

In late April 2026, nineteen enthusiastic volunteers planted the trees in celebration of Earth Day. The morning began with a demonstration of planting-hole size and shape, proper planting depth, loosening the root ball, and backfilling.

Zoo staff played a key role by marking planting sites and delivering trees to each location, mulching and watering each tree, and distributing stakes and helping install them.

Six-Month Results

Six months after planting, 29 of the 30 trees remain alive—a 97% survival rate. One of the Maple trees died within the first month and was most likely due to poor soil conditions including sever compaction and lack of drainage. Most trees grown in air-pruned containers showed noticeable first-season growth, exceeding what is typically see in larger, closed-container trees. This was especially encouraging given the exceptionally warm, dry, windy summer.

Air-Pruned Roots: Benefits and Watering Needs

Root Development and Establishment

Air pruning prevents roots from circling and encourages dense branching, helping trees establish more quickly. It also virtually eliminates the risk of future girdling roots, a common cause of tree decline and death years after planting. The air-pruned root systems were notably more fibrous than those of traditional container-grown trees.

Watering During Establishment

The greater root mass dries out more quickly, however, so these trees need more watering until they establish.