Colorado Soils, Amendments and Fertilizer

Summary at the Top

Improve your garden soil for better plant root growth by adding Organic Matter

Use Natures Yield Organic Compost 1-2″ deep tilled or spaded into a depth of 6-8″.  Or incorporate compost into soil at planting time – hole by hole/ plant by plant.

Use Natures Yield Outdoor Planters Mix for planting in raised beds or large outdoor containers.  Annuals, perennials, vegetables all good.

Use Earth Essentials Top Soil for filling in low spots in the lawn and garden

Use Premier ProMix Potting Soil for planting into containers indoors and outdoors.  Houseplants, annuals, perennials, vegetables.

Use Jacks soluble fertilizer for liquid fertilizer applications with a watering can or hose end applicator in containers and in garden beds.

Use Fertilome or Espoma for dry fertilizer applications in garden beds.





Soil considerations are twofold:

  • Soil structure- physical properties
  • Soil nutrition- fertility
Soil Structure

Soil is a mixture of:

  • microscopic to larger forms of life (like earthworms)
  • air
  • water
  • decomposing living matter, aka organic matter
  • different-sized soil texture particles or pores (there are three main types).

Particle sizes:

  • sand, the largest soil particles like golf balls
  • medium-sized particles of silt, represented by marbles.
  • 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).

Typical compacted, unamended landscape soil (which is common in Colorado):

  • 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 in our area.

Plant roots need a good balance of all 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.

Improve your soil.

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 fully decomposed organic matter, like compost, manure, amendments and decomposing living matter like leaves or grass.

What does Humus do for soil?

  • Microorganisms break down the organic matter in the composting process releasing nutrients to the soil to feed the plants.
  • Binds 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.
  • sandy soil pores are reduced, which improves holding moisture and nutrients.

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.  See Creek Side handout for additional info.

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.

Soil/ Plant Nutrition – Fertilizers

Plants need additional nutrients in the form of fertilizer to grow to their potential because they are lacking in the native soils.

Nutrients from water & air – carbon, hydrogen, oxygen

What is soil fertilizer N-P-K?

  • Nitrogen – promotes vegetative growth i.e., stems and leaves.
  • Phosphorus – promotes all growth especially root growth.
  • Potassium – promotes flower & fruit growth.
  • Secondary nutrients – Calcium, Magnesium, Sulphur
  • Minor elements – Manganese, Iron, Boron, Molybdenum, Copper, Zinc
  • Soil pH – affects each nutrient availability to plants

Where does fertilizer come from?

Synthetic forms – straight chemicals & blends

  • Calcium nitrate, ammonium sulphate, potassium nitrate
  • Jacks, Fertilome, Miracle-Gro
  • Readily available to the plants
  • Relatively less expensive
  • Easy to apply.

Organic forms – from something living – animal or plant.

  • Cow & sheep manure
  • Composted bark, tree leaves, lawn clippings
  • Blood meal, Bone meal, Feather meal, Bat guano, Seaweed kelp
  • Fish emulsion, Bio-Tone, Neptune’s Harvest, Fox Farm
  • Mycorrhizae – beneficial fungi colonize roots and aid in nutrient uptake
  • Takes longer to be available because it must break down to release nutrients.
  • Lasts longer in the soil, remains available longer.
  • Nurtures soil health

How is fertilizer applied to the soil?

Liquid- liquid or granular concentrate diluted in water and applied to the soil.

  • Easy to apply with watering can or hose end applicator.
  • Fast acting- easily available to plants because it is already dissolved in water.
  • Will leach more quickly.

Solid – granular incorporated into the soil

  • Takes longer to become available.
  • Lasts longer.

Which fertilizer should I use?

Don’t get hung up on the numbers.  Follow the recommended rate.

  • Choose your application method – liquid or dry – Jacks for liquid, Espoma or Fertilome for dry
  • Choose your preferred source – synthetic or organic.
  • Consider the application area – ground/ landscape or containers.
  • Consider the crop – flowers, vegetables, shrubs/ trees, lawn.
  • Consider the time of the season/stage of the crop – early or late, vegetative or flowers & fruit.

Check with your Green Team staff for a recommendation