The greatest challenge to the urban Front Range gardener lies in the first foot of topsoil where most plant growth occurs. During home construction, soil on the building site is graded, pushed around, and often removed leaving a compacted layer of clay subsoil which drains poorly and refuses to allow the root systems of plants to efficiently absorb oxygen, nutrients, and water. This soil often has a high pH and lacks organic matter and beneficial microbes. Plants don't like these conditions so it's not surprising that approximately 80% of our urban garden problems begin with poor soil conditions.
The trick to working with these challenging soils is to improve soil tilth or texture and adopt planting methods that will encourage healthy growth. One approach is to use raised beds for vegetables. Raised beds are created by simply mounding soil higher than surrounding walkways or by enclosing these mounds in a wooden frame construction or rock edging. Since raised beds warm up and dry out earlier in the spring the ardent gardener can get a head start in preparing the soil for planting. Clay soils are stubborn and must be loosened by tilling or double digging and then amended with organic material to improve water and nutrient- holding capacity, aeration, and drainage. It is recommended that you incorporate three cubic yards of well-composted organic matter into each 1000 square feet of garden area. Another way to look at it is to add approximately 1-inch of compost over the soil and then mix it well. Sphagnum peat is a good choice for an amendment but avoid Colorado peat that is generally higher in pH and finer in texture.
Once your soil is properly prepared you can organize the beds. A good rule of thumb is to make them no wider than four feet to allow easy access to the plants. Think about arranging your plantings in a grid design with equal spacing between plants and rows. It's important to include 18-24 inch paths between the beds to reduce soil compaction in the growing area. Mulching these walkways with gravel, bark, wood chips, or grass clippings will reduce weeds and lend a finished look to the garden. Be diligent about keeping your beds watered either by drip irrigation or soaker hoses and if time allows, have your soil tested prior to cultivation to determine its nutrient levels and fertilization requirements. When properly prepared, raised beds will increase your harvest because there is no wasted space in the garden and the soil is in better-than-average condition to support denser growth.
For more information see Fact Sheet #7.220 Colorado Gardening: Challenge to Newcomers, #7.235 Amendments: Choosing a soil amendment, #7.222 Soil: The Key to Successful Gardening, and #0.507 Soil, Water, and Plant Testing. You can also call Planttalk Colorado toll free at 1-888-666-3063 and request recording number 1812, Raised beds vs. rows.
Q: My landscape designer has discouraged me from planting aspens and yet I see them growing in many yards around Fort Collins. Why are they not recommended along the Front Range?
A: Aspens are more comfortable in the higher altitude environment of the mountains where the soil is slightly acidic, drainage is good and temperatures are slightly lower. Growing them at 5,000 feet stresses them and they become more susceptible to insects and diseases and have a shorter life expectancy. If you bring aspens into your landscape, your success rate will be higher if you properly amend the soil prior to planting and locate the trees on the north or northeast side of your property.
Q: Can I use fresh manure on my vegetable garden?
A: No! Fresh manure should not be used in vegetable gardens because there is the possibility of transmitting E. coli and other human pathogens. If you want to use manure be sure that it has been well composted and apply it to the garden at least four months prior to harvest. Manure can also increase the salt level and raise the pH of your soil--two conditions that limit plant growth so you might want to test the salt content of the manure before application.
The authors have received training through Colorado State University Cooperative Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.
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