Soil-less Mix Interpretation

Interpretation of Bark Soil-less Mixes

Mineral Analysis Insufficient Sufficient Supraoptimal
Nitrate-Nitrogen (NO3-N), ppm <50 50-200 >200
Phosphorus (P), ppm <10 10-30 >30
Potassium (K), ppm <25 25-50 >50
Magnesium (Mg), ppm <10 10-50 >50
Calcium (Ca), ppm <10 10-50 >50
Soluble Salts   Optimum  
Electrical Conductivity, mmhos /cm   0.7 – 3.0  
Total Dissolved Solids, ppm   448 - 1920  
pH   5.0 - 6.5  

Interpretation of Peat Based Soil-less Mixes

Mineral Analysis Insufficient Sufficient Supraoptimal
Nitrate-Nitrogen (NO3-N), ppm <40 40-300 >300
Phosphorus (P), ppm <3 3-18 >18
Potassium (K), ppm <60 60-350 >350
Magnesium (Mg), ppm <30 30-140 >140
Calcium (Ca), ppm <80 80-400 >400
Soluble Salts Optimum
Electrical Conductivity, mmhos /cm   0.8 - 5.0
Total Dissolved Solids, ppm   512 - 3200
pH
5.3 - 6.5

Important Concerns

  • Plants of the Ericaceae family, e.g., azaleas and salt sensitive plants, require only one half the level of mineral nutrients and can tolerate only one half the soluble salts shown on the table above.
  • Plant growth will be enhanced if additional nutrients are added in cases where the mineral analysis is low.
  • Plant growth may be enhanced if nutrients at the lower end of the sufficient range are increased in the media.
  • Plant growth will not be enhanced by the additional rates of nutrients, which are already in the supraoptimal range.
  • Lab results for nitrate-nitrogen may be artificially high if a slow-release fertilizer is present in the mix.
  • Soluble salt values exceeding the optimum range indicate the potential for excess salt accumulation, which may be toxic to plants.