Colorado Gardening for New Comers

June 24th, 2021

Gardeners who are patient, know how to select plants that will do well, and manipulate the soil and microclimate, will be amply rewarded.

Gardening in Colorado can be challenging. The average elevation of the state is 6,800 feet. Three-fourths of the nation’s land above 10,000 feet is within its borders. Sunlight is frequently of high intensity and the humidity generally is low. These features, along with rapid and extreme weather changes and 

frequently poor soil conditions, make for challenges in growing plants. 

Newcomer’s Dilemma 

Newcomers to Colorado often have trouble getting plants to thrive or even survive. More often than not, they previously gardened where “you stick a plant in the ground and it grows.” Often, those from northern states such as Minnesota or Michigan are puzzled why certain trees that did well for them there do poorly in Colorado. 

Temperature is not the only factor that determines plant survival in Colorado, for rarely is extreme cold the limiting plant growth factor. Combinations of low humidity, drying winds, and physical properties of the soil influence how well plants perform here. 

Soil Properties 

Many of our population centers are on heavy, clay soil. These soils have poor aeration that limits root growth. Thus the ability of plants to replenish water loss brought about by low humidity and prevailing winds is limited. Adding more water to such soils further complicates the problem because the water that is added reduces the amount of air in the soil and causes oxygen starvation to the roots. Little can be done to modify humidity and wind, so the obvious solution is to improve the soil. 

Salt Accumulation 

Soil modification is a problem in our semiarid, highly alkaline soils. Organic matter, if added in large amounts all at once, can provide for a more porous soil. However, this practice can lead to the accumulation of natural, soluble salts. Unless the soil is porous so that salts can be leached away with water, the salts tend to accumulate in the amended soil layer. The soluble salts may remain in the organic matter much like water remains in a sponge. Rapid evaporation may concentrate the salts in the root zone, where they can injure plant roots. 

A solution to this problem is to slowly, over a period of years, improve the soil tilth. An alternative to leaching the salts and improving the soil is to choose plants more tolerant to saline soil conditions. For instance, instead of planting a pine knowing that it would do poorly under such conditions, one may have to settle for a juniper.

Iron Problems 

The name Colorado comes from the Spanish words “color rojo,” meaning color red, referring to the dominant red soils. The red color is due to high amounts of iron in the soil. Yet, a yellowing condition in certain plants, known as iron chlorosis, is brought about by an iron deficiency in the plant. Colorado’s highly calcareous (high calcium) soils tie up the iron in a form unavailable to the plant. 

Trees with high iron requirements such as pin oak, silver maple, and Washington hawthorn perform poorly in Colorado’s calcareous soils. Making iron more available is not easy and usually not economical. Adding available forms of iron such as iron sulfate to the soil is, at best, a temporary measure. The soil itself will quickly cause much of the added iron to become unavailable. The best alternative is to select plants tolerant of Colorado’s alkaline soil. Instead of pin oak, choose bur oak, or Norway maple instead of silver maple, etc. 

The Brighter Side 

Up to this point, gardeners might want to throw up their hands and say, “What’s the use?” But there is a brighter side. 

Colorado’s many days of sunshine, while leading to some problems already mentioned, enables gardeners to grow some of the best flowers in the nation. The high light intensity produces strong-stemmed plants and flowers with extra brilliance. 

Vegetables, with some care in variety selection, grow luxuriantly in most locations. Winter sunlight melts snows at lower elevations, reducing snow mold diseases in lawns. Growers of roses, carnations, and other greenhouse crops produce some of the best cut flowers in the world. 

The cool, crisp nights and warm days produce the nation’s best lawns. These same climatic conditions enable the home gardener to produce excellent potatoes, cabbage, lettuce, broccoli, cauliflower, and other cool-season vegetables. 

The lower humidity not only helps to make the cold days seem less cold and hot days less hot but discourages many landscape plant diseases that are common in more humid areas. Perhaps the brightest side lies in the challenging problems in growing plants. Gardeners who are patient, know how to select plants that will do well, and manipulate the soil and microclimate, will be amply rewarded.