The BEST Approach We’ve Found to Fertilizing Trees In Denver

Tree Fertilization - Fielding Tree and Shrub Care arborist Denver


Are you ready to take your landscaping to the next level? Give your trees and shrubs the nutrients they crave by applying the best new fertilizers! Watch them transform from lackluster into vibrant and lush greenery when spring arrives.

What Is Tree Fertilizer?

Tree Fertilizer is a compound of nutrients that are applied to trees to keep them healthy and strong. Typically, fertilizers capture nitrogen from the air and put it in the soil. Tree fertilizers improve the quality of the soil, adding nutrients where they can be taken up by the tree’s roots.

The key nutrients a tree needs are nitrogen, phosphorus, and potassium. These are the nutrients found in tree fertilizers. Fertilizers can be solid or concentrated and applied in several different ways. The type of tree or shrub, type of soil, season, and other environmental factors will determine which tree fertilizer is appropriate.

Do My Trees Need to Be Fertilized?

Asking “Do my trees need to be fertilized?” is like wondering “Do I need to take vitamins?” The answer (for one reason or another) is probably yes. Even if you eat a healthy diet, your daily diet might not provide key nutrients your body needs to stay in tip-top shape. Opting to take a multi-vitamin covers all your bases and keeps your body balanced and healthy. Fertilizers are like vitamins for trees! They replenish essential minerals and keep trees happy and healthy.

Signs that your tree is not getting enough nutrients:

  • Shorter than normal annual twig growth
  • Undersized leaves that are fewer in number
  • Dead branches and branch tips
  • Leaf veins darker than leaf margins
  • Leaves any other than dark green, such as yellow or purple

Generally speaking, abnormally small leaves and short new twig growth are strong indicators of a need for fertilizer. Yellowing leaves is one of the most common symptoms of a lack of soil nutrients. Chances are your soil isn’t perfectly balanced with the nitrogen, phosphorus, and potassium your trees need. Your trees might look OK, but with a boost from the right fertilizers, they can look radiant! Our arborists will start by testing your soil to find where nutrients are deficient.

Managing Your Soil

What has soil got to do with it? Everything! Managing soil pH is a science. When done correctly, managing your soil will result in the healthiest trees and shrubs possible.

A soil test is a quick and inexpensive way to get specific information on the potential for tree response to agricultural limestone and to phosphorus, nitrogen, and potassium fertilizers. Doing a test will also give an accurate basis for deciding how much of those materials to add when they are deficient.

A soil sample can sometimes be challenging to collect since most nutrient-absorbing roots of trees are in the upper 6 inches of the soil and may extend two or three times beyond the radius of the crown. To figure out the nutritional needs of your trees, it is also important to consider soil and moisture conditions; the species, age, and strength of the tree. The test will help determine what kind of fertilizer is right for your trees and how much they need.

Here are some details on soil pH to help you make sense of your soil test:

  • Unaltered Denver soils commonly range in pH from 6.8 to 7.2.
  • Most deciduous trees and shrubs do best within a soil pH range of 5.5 to 6.8. Red maples, oaks, junipers and most conifers like pines, firs and hemlocks prefer a pH of 5.5 to 6.0.
  • Some conifers can tolerate higher levels; for example, yews prefer a pH of 6.0 to 7.0.
  • Deciduous plants, including lilacs, pink or white hydrangeas, and some viburnums, will tolerate a higher level of pH. Big leaf hydrangea is unique in its response to soil pH, producing blue flowers in low-pH (acid) soils and pink flowers in high pH (alkaline) soils.
  • Incorporating 5-10 lbs. of ground limestone per 100 square feet of area will generally raise pH one-half to one unit on the pH scale, but a more precise recommendation can be determined by a soil test. It is best to incorporate lime into the soil to a depth of 6 inches before planting, since surface applications are slow to change pH levels.

Benefits of Fertilizing

  • Prevent Disease: When you take vitamins, your body can better defend itself from viruses and bacteria. You are less likely to catch a cold or stomach bug. Fertilized trees have the same strength. They can fight off tree diseases like Cytospora Canker, Bacteria Wetwood, Marssonina Blight, and Powdery Mildew that are prevalent in the Denver area. Trees that are injured, stressed, or lacking nutrients become weak and susceptible to disease.
  • Prevent Pests: Trees that are strong and growing vigorously are also less susceptible to attack by insects. The Emerald Ash Borer, IPS beetle, Ash/Lilac Borer, and Japanese Beetle are just a few of the pests plaguing trees in Denver. Fertilizer can improve your tree’s resistance to infestation.
  • Stimulate Growth: The right fertilizer will give your tree a boost in needed nutrients. This can result in stimulating mild-rapid growth. If you desire a fuller canopy or greener lush leaves, fertilizer will help you reach your goals.

What Are The Best Fertilizers For Trees?

Remember, nitrogen, phosphorous, and potassium and the three nutrients trees need to thrive. The nutrient most used in fertilizers is nitrogen. It increases growth rate and causes plants to become vibrantly green. Plants that are established and only add a little bit of growth each year or have small leaves may have nitrogen deficiency. Nitrogen has several forms and can be converted or lost in the soil environment, so there is no conclusive test for it. Our arborists may recommend a nitrogen fertilizer based on observation research and experience with how trees respond to added nitrogen.

Phosphorus fertilization is only effective for trees where the soil levels are very low. Most soils are already high in phosphorus. Fertilizer containing phosphorous should not be used unless recommended by a soil test. It is not uncommon to see an excess of phosphorus. This can be carried by stormwater runoff into surface waters, where it can lead to problems with water quality.

Potassium is typically low in Denver soils. It should be included in your plan for fertilization along with nitrogen. The amount should be determined by a soil test. Areas of dead tissue along leaf edges may be a symptom of potassium deficiency.

Denver has alkaline soil which is unusually high in iron. Unfortunately, iron is not a nutrient that is particularly helpful to trees and shrubs. We recommend these new tree fertilizers to treat the unique nature of the challenges facing Denver’s soil:

Bi-Annual Soil Injection Service

  • Promotes vigorous root growth and deep-root watering, while providing additional micro-nutrients that may be limiting in the soil substrate.
  • Deep-Root system is under higher pressure than traditional hose, thereby providing some aeration which breaks up soil compounds.
  • Product used will also lead to vibrant foliage, healthier limbs and will boost the natural defenses of the tree. Especially recommended during a year when trimming operations have occurred to assist with healing of pruning wounds.
  • We recommend a Bi-Annual Application, with each cost below being per treatment (once in Spring and once in Fall). We will continue biannual application until instructed to discontinue the service by the client.
  • Contains chelated iron, soluble potassium, magnesium, manganese, humic acid, Trichoderma fungi, soluble sea kelp, yucca plant extracts, and amino acids to “energize” the microbial activity in the ground and promote cell division and lateral bud development as well as delay the aging process of plant tissue.
  • Our unique formulation of ingredients includes diverse strains of beneficial fungi (Trichoderma). All these factors are well known to provide a major benefit to plants promoting vigorous root growth and enhance the overall general conditions of the plant environment.


  • New Addition for 2019! This is specialty charcoal made from woody material, used as an amendment to improve soil quality.
  • When used as a soil amendment, it provides numerous benefits, including water and nutrient retention.
  • Biochar particles have very large and absorbent surface areas, providing sites that water and nutrients can adhere to. This helps sandy soils hold more water, and opens up space in clay soils for root growth.
  • Fertilizer applications are more efficiently used when combined with biochar, since the nutrients are held in place for tree roots to use rather than getting leached away by rainfall. The biochar surface is filled with water and nutrients during fertilization, natural rainfall, and plant decomposition.
  • The biochar acts as storage, holding that material until the plant roots need it.
  • Biochar recycles urban wood waste! Biochar helps fight climate change by taking carbon out of the atmospheric cycle and by helping trees grow better.

When Is The Best Time To Fertilize Trees In Denver?

The best time to fertilize trees runs from late fall, when leaves have all dropped, through the winter and into early spring. Fertilization needs to happen before new growth begins to start in mid-spring. The benefit of applying fertilizer in the fall is that it has more time to penetrate the soil and tree roots can fully absorb it. Fertilizer applied during the winter can be absorbed by the roots even during the cold and is available to the plant for growth in the spring.

Take advantage of these winter months while the demands of yard work and landscaping slow. Focus on treating your trees now with care and attention so that come spring they will be the envy of your neighbors!

Team up with our Fielding team to test your soil today! Get a consultation and start planning your custom fertilization treatment for healthier, happier trees.