Environmental Tolerance

Tolerance is not a yes or no. It is a range, and a planting site is a stack of conditions the plant has to clear all at once — soil chemistry, available water, hours of direct sun, winter low, wind, and how fast the ground drains. A plant can be perfect on six of those and fail on the seventh.

The one that catches people here is soil pH. Ground across most of Delta and Montrose counties runs alkaline, commonly in the 7.5 to 8.2 range. At that pH, iron and manganese are present in the soil but chemically locked up where roots cannot take them, and the plant starves in the middle of plenty. It is the reason a long list of trees sold as dependable elsewhere are a poor bet here.

These are the tolerances we sort by, and what each one means on ground like this.

Alkaline-Tolerant
Handles soil above pH 7.5 without going chlorotic. On the Western Slope this is less a feature than a requirement, and it is the single most useful filter on a plant list.
Acid-Loving
Needs soil below about pH 6.5 — which this valley does not have. Read this as a warning label rather than a feature, and plan on a container or a dedicated bed if you want one anyway.
Well-Drained Soil
Roots need air as well as water, and will rot without it. The most common line on a plant tag, the most often ignored, and in heavy ground here it kills more plants than drought does.
Drought-Tolerant
Gets by on little water once established — and establishment takes two full seasons of regular watering first. Drought tolerance is earned, not delivered with the plant.
Sun-Loving
Wants six or more hours of direct sun. Worth knowing that sun at 5,000 to 6,500 feet in dry, clear air is considerably stronger than the same hours at low elevation.
Shade-Tolerant
Grows in less than about four hours of direct sun. Worth separating from dry shade under mature trees, which is a harder site than shade alone and the hardest spot in most yards.
Cold-Hardy
Survives the winter lows here — most of this area is USDA zone 5 to 6, varying with elevation. The zone number is an average, and it says nothing about the late frost that does most of the damage.
Heat-Tolerant
Holds up through hot, dry summer afternoons. Here that means dry heat plus high-altitude sun plus wind, which is a harder combination than the temperature alone suggests.
Salt-Tolerant
Handles salt at the roots or on the foliage. Two sources here: de-icing salt along drives and roads, and salts that accumulate in the soil because there is not enough rain to flush them out.

Once you can see the pH problem you will see it everywhere in this valley. Leaves gone pale yellow while the veins stay green, worst on the newest growth at the tips — that is iron chlorosis, and silver and red maple, pin oak, river birch and quaking aspen are where it shows up most. All of them are excellent trees somewhere with different dirt.

Treatment exists and it is a treadmill. Chelated iron greens a plant up for a season, sometimes two. It does not change the pH, so it repeats for the life of the plant. A soil acidifier moves the number temporarily and then the native ground and the irrigation water pull it back. Which is why the plant list is the answer and the amendment is not.

Two others are worth knowing before you shop. A hardiness zone is an average winter low, so it tells you nothing about a hard freeze in the middle of May — and a late frost is what actually does the damage here, catching a plant after it has broken dormancy and spent its energy on new growth. And drought tolerance is earned rather than issued: a drought-tolerant plant is drought-tolerant once its roots are deep, and getting there takes two full seasons of regular water.

None of these decides anything on its own. A site is the combination, which is why a plant list that worked beautifully at a friend's place in Grand Junction can struggle at yours, twenty minutes away and eight hundred feet up. If you are not sure what your site actually is, that is the first thing we work out — soil, water source, drainage, exposure — and the plant list comes after it rather than before.

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