Agricultural Service Laboratory
Clemson University

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 COMMENTS:

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.