Knowledgebase

Too high Nitrates #947465

Asked October 21, 2026, 3:34 PM EDT

I have had a perennial garden for about 12 years in Breckenridge CO at 9300 feet. It has been beautiful for all those years. This past summer about 1/3 of my plants did not come up and the remaining plants were spindly and either had no flowers or a few flowers. I sent in soil samples to CSU in the spring and the results indicated very high organic matter, Very high nitrate and very high phosphorus. I watered the garden during the summer and did NOT fertilize thinking I had over fertilized. I sent in another soil sample just a few weeks ago and organic matter is still very high, nitrate is now low and phosphorus is still very high. I also have slightly alkaline soil ,ph and low soluble salts. Potassium is very high. Sulfate is also very high. I am at a loss about how to or if I should treat the soil before the snow falls. The comments on the test say apply 1.0 lbs of nitrogen per 1,000 sq ft 3 times during the growing season. Phosphorus, potassium and sulfur levels are above or adequate for flowers. This makes no sense to me to add nitrogen. What should I do, if anything now and then again the spring. If we have a good winter, the garden will sit under 1 to ft of snow.

Summit County Colorado

Expert Response

Ferol, you have a memorable name. I think you may have attended the Master Gardener class pre-COVID. Is that possible? Anyway, hi! Dan Schroder here. 
Thank you for your write up. You should not add any nitrogen or other fertilizers to this garden right now or in the spring. The test results are in error because it is a software output generated by baseline fertilizer recommendations that does not take into account your historic situation. Your reports indicate that your organic matter and phosphorus levels remain very high. After 12 years of gardening—especially in mountain environments where organic matter breaks down more slowly—heavy accumulation can occur. Your plants might be spindly because of organic matter and phosphorus build up or when nutrient ratios become severely unbalanced, it can disrupt plant health. Excess nitrogen and salts from long-term accumulation can cause lush, weak, spindly growth, restrict root development, or block the uptake of other micronutrients, causing plants to fail or lack flowers.

Action Plan: What to Do Now and Next Spring
1. Right Now (Before the Snow Falls)
  • Do Nothing: Do not add any fertilizers, compost, manures, or amendments.
  • Let Nature Take Its Course: Allow the garden to go dormant under its 1 to 2 feet of winter snowpack. Snow cover is actually beneficial; as it slowly melts in the spring, it will gently leach any remaining excess surface salts or residual soluble nutrients out of the immediate root zone.
2. In the Spring
  • Hold the Fertilizer: Skip any nitrogen or phosphorus applications. Your soil already holds an abundance of legacy phosphorus, and adding more will only worsen nutrient antagonism.
  • Ease Up on Organic Amendments: Avoid adding any more compost or organic matter next spring, as your organic matter percentage is already at the top end of what perennials prefer.
  • Monitor and Flush: When the snow melts, give the bed a thorough, deep watering (if spring rains are light) to help naturally leach any lingering excess mobile nutrients deeper past the root zone.
  • Observe Plant Recovery: Many established perennials suffering from a temporary nutrient lockout or root stress bounce back once the soil microbiome stabilizes and the excess nutrient flush normalizes.
This information comes from:

Colorado Master Gardener Program — Soil Savvy & Property Guidelines (Table 1) CSU Soil, Water and Plant Testing Laboratory — Interpreting a Soil Test Report CSU Extension Fact Sheet — Understanding Fertilizers
  • CSU Extension Fact Sheet — Soil Tests













    • An Ask Extension Expert Replied October 21, 2026, 7:42 PM EDT

    Loading ...