Colorado Garden Soil Improvement

A little understanding of our weather conditions and working in our dry, limiting soil properties will help you improve your garden soil and make smart plant choices this gardening season.

Soil is a fascinating mixture of microscopic to larger forms of life (earthworms are good), plus varying amounts of air, water, decomposing living matter, aka organic matter, and different-sized soil texture particles or pores (there are three main types).

Soil Particle Sizes

Think of sand, the largest soil particles like golf balls; next are the medium-sized particles of silt, represented by marbles; and finally clay, the smallest particles, are like layers of pennies. Putting them all together with different percentages of the pore particles indicates how well plant roots will grow and thrive.

Well managed western soils have 25% air, 25% water (pore spaces), 1-5% organic matter (dead & living), and 49% mineral solids, comprise the (solid particles).

A typical compacted, unamended landscape soil (which is common in Colorado), has 10% air, 20% water, 1% organic matter and 69% mineral solids. Not the best growing foundation for plants.

Moisture drains more slowly in smaller pore spaced clay soils, so drowning plant roots happens easily. Heavy clay soils are very common in our area. On the opposite end, sandy soils with large pore spaces are fast draining, lose nutrients and dry out quickly are not as common.

Water and Air Spaces

Plant roots need a good balance of all of these particles to allow water, air and organic matter to support existing landscape plants and your new plantings this spring.

Adding soil amendments such as organic compost allow for better absorption of water and improved water holding capacity of the soil.  Organic matter also provides beneficial nutrients to plants and air for deep root growth.

The first step in correcting soil is to figure out what you have.

On-the-spot, low-tech structure feel test: squeeze a small handful of soil, add a little water. If it sticks together and makes a smooth, shiny ball that doesn’t break apart, the soil is clayey. If the ball is less dense, easier to move in your hand, it’s a combination of sand and silt. A loose ball that easily breaks apart generally has more sandy particles.

Add Organic Matter

Whether you have overly clayey or sandy soil the best way to improve it is to add organic matter (OM) which eventually becomes humus.

Humus is the result of decomposed organic matter (a word used interchangeably with compost, manure, amendments and decomposing living matter like leaves or grass).  The microorganisms break down the organic matter releasing nutrients to the soil to feed the plants.

Humus has the added bonus of binding the three different soil pore sizes, which improves pore space. Clay pores are opened up, resulting in better soil drainage and air to plant roots, while sandy soil pores are reduced, which improves holding moisture and nutrients.

Natures Yield Organic Compost

Bagged soils like, Natures Yield Organic Compost can be added as OM.  Or OM may be purchased in larger quantities (by the cubic yard) or added from a homemade compost pile. Typically a layer of 1”-2” is applied to the top of the soil and tilled to a depth of 6”-8” deep.

Natures Yield Outdoor Planters Mix is used for filling in ground level planters like raised beds.  Essential Earth Top Soil is used for filling in holes or raising low spots in the lawn or garden.

Caution: Too much of anything, including OM, is not good (over five percent is too much), often interfering with air, water and nutrient penetration to the soil. Too much organic matter can rob plants of nutrients during the decomposition process.

A soil test may be performed for brand new planting beds, where it is important to establish a baseline on salt levels, soil pH, soil texture and other nutrients including nitrogen, phosphorus and potassium. Inexpensive soil test kits from CSU Soil Testing Lab are available for pickup from Creek Side Gardens.

Compost piles

Compost can be used as a soil amendment and mulch.  Composting yard waste recycles nutrients back into the yard and saves landfill space.  A combination of brown and green materials along with water, nitrogen, aeration and beneficial micro-organisms are necessary to make the process happen.

Potting Soils

These soils, like Creek Side’s ProMix are especially formulated for growing plants in container gardens.  They are a blend of peat moss and other ingredients that will result in optimal water holding and aeration properties for container growing.  ProMix is the same potting soil that Creek Side uses for all their greenhouse growing.


Mulches are applied to the surface of the soil to help conserve moisture in the soil and keep the soil temperature cool.  Plus they add landscape appeal.  Bark mulches like Western Red Cedar, Redwood Bark Nuggets and Brown Harvest Mulch are applied 2-3” deep.  Stone or rock mulches may be used as well.


Although OM will release plant nutrients to the soil as they decompose, additional fertilizer applications should be made for plants to realize their full potential.  Consider a dry granular application at planting time or in the spring.  The formulation could be regular or organic.  If the soil is covered in mulch which would make the dry fertilizer application difficult to scratch into the top of the soil, consider a liquid fertilizer application of Jack’s General Purpose Fertilizer.  Small applications may be applied with a watering can.  Use Jack’s hose end applicator for larger jobs.