Soil Testing and Plant Diagnostic Services

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Keith Hawxby photoGreenhouse growing media analysis

Why sample

Testing greenhouse media provides an assessment of the material to adequately provide plant nutrients and provide a good rooting environment, i.e. low salt content and adequate pH.

Submitting samples

When submitting a sample to the lab the sample information form should be filled out accurately. Include a check for the amount due payable to MU Soil Testing, unless you have an account with us. If you have an account with us fill in the firm and outlet number and we will bill you at the end of the month.

Samples can be submitted directly to the lab or a county extension centers.

Soil and Plant Testing Laboratory
23 Mumford Hall
Columbia, MO 65211
Phone: 573-882-0623
Fax: 573-884-4288

A minimum of one quart of media is needed for analysis.

Greenhouse media analysis sample information forms can be picked up at the MU Soil and Plant Testing Laboratory free of charge or printed from the Web .
Greenhouse media analysis information form

Available tests and fees

See our charges.

In the labTurnaround time

  • Soil sample analysis
    1.5 working days after samples are received in the lab
  • Plant, compost, greenhouse media and water analysis
    4 to 5 working days after samples are received in the lab

If samples are mailed allow time to and from the lab. Results of samples submitted through county extension offices are mailed first to the county agronomist or horticulturalist for comments or individualized recommendations. The county then mails the recommendations to the person submitting the sample.

Soil test reports can be emailed on request at no charge or faxed for a nominal fee.

Interpretation and recommendation guidelines

The desirable pH, soluble salt and nutrient levels for greenhouse or soil-less media vary by the greenhouse or nursery crop and by the management practices used. The ratings and recommendations given below are general guidelines for results obtained from water or DTPA saturation extracts.

Table 1
Test result interpretations*


Low rating Acceptable rating Optimum rating High rating Very high rating

Soluble salt (mmho/cm)

0 to 0.75 0.75 to 2.0 2.0 to 3.5 3.5 to 5 > 5.0

Nitrate-N (ppm)

0 – 39 40 to 99 100 to 199 200 to 299 > 300

Phosphorus (ppm)

0 to 2 3 to 5 6 to 10 11 to 18 > 19

Potassium (ppm)

0 to 59 60 to 149 150 to 249 250 to 349 > 350

Calcium (ppm)

0 to 79 80 to 199 > 200    


0 to 29 30 to 69 > 70    
*Taken from Warneke, D. 1998. Greenhouse Root Media.
Adequate micronutrients ranges (using the DTPA Extraction Method) are: boron, 0.7 to 2.5 ppm; copper 0.5 to 1.5 ppm,  iron, 15 to 40 ppm manganese, 5 to 30 ppm; and zinc, 5 to 30 ppm.

Modifying pH

It is best to modify greenhouse media before establishing plants. Some rapid corrective measures can be used to adjust media that already contain plants. However, amendments such as iron sulfate and hydrated lime – used to change pH – will burn most plants. Apply amendments only to the root medium. Rinse plants with water if material comes in contact with plant surfaces. Some plants may be sensitive, so test a small area or a few plants before treating a large area. A pH adjustment of 0.5 to 1.0 unit is rapid, but effects are short lived. Recheck the pH within a week and reapply if necessary.

The effectiveness of amendments and their application rates will vary with different media. The amount of change is dependent on the type, concentration, and fineness of the material used and the buffering capacity of the greenhouse media. The attached tables contain recommendations that are approximations.

Table 2
Approximate rates of materials to modify pH of a root medium*

Amendment For bench soils
lb/100 sq ft
For potting soils
lb/20 bu or 1 cu yd
For potting soils
oz/2.5 bu
Rate of pH change Length of change
To lower pH 0.5 to 1.0 unit
Finely ground sulfur 0.5 0.25 0.5 slow long
Aluminum sulfate 3 1.5 3 rapid short
Iron sulfate†‡ 3 1.5 3 moderate short
To raise pH 0.5 to 1.0 unit

Ground limestone

5 2.5 5 moderate long
Dolomitic limestone 5 2.5 5 moderate long
Hydrated lime# 2 1 0.75 rapid short
*Adapted from B.E. Whipker. Iowa State University.
Can be applied as a soil drench in enough water to cover 100 sq ft bench area or equivalent soil area of potted crops.
Iron sulfate will increase a root media’s EC and may release toxic levels of micro-elements from the root media’s exchange sites.
#Hydrated lime is corrosive. Avoid contact with skin and metal. Hydrated lime may displace ammonium from the root exchange sites of the root medium into the soil solution causing root injury. Avoid using hydrated lime if high levels of ammonium fertilizer are present in the root system.

Table 3
Approximate amounts of sulfur or dolomitic limestone required to modify the pH of various types of root media to pH 5.7 from a stated beginning pH.*

Beginning pH 50 percent peat and 50 percent sand 50 percent peat and 50 percent bark 100 percent peat
Sulfur required to lower pH to 5.7
7.5 1.7 lb per cubic yard of medium 2.0 lb per cubic yard of medium 3.4 lb per cubic yard of medium
7.0 1.2 lb per cubic yard of medium 1.5 lb per cubic yard of medium 2.5 lb per cubic yard of medium
6.5 0.8 lb per cubic yard of medium 1.0 lb per cubic yard of medium 2.0 lb per cubic yard of medium
Dolomitic lime or equivalent amount of calcium to raise pH to 5.7
5.0 1.7 lb per cubic yard of medium 2.5 lb per cubic yard of medium 3.5 lb per cubic yard of medium
4.5 3.7 lb per cubic yard of medium 5.6 lb per cubic yard of medium 7.4 lb per cubic yard of medium
4.0 5.7 lb per cubic yard of medium 7.9 lb per cubic yard of medium 11.4 lb per cubic yard of medium
3.5 7.8 lb per cubic yard of medium 10.5 lb per cubic yard of medium 15.5 lb per cubic yard of medium
*Adapted from M.L. Albrecht. 1991. Plant nutrition, fertilizers, water quality and pH. Kansas Flora. 9(3):3-7.
Additions of more than 10 pounds of dolomitic limestone per cubic yard often causes micronutrient deficiencies.

Rapid adjustment of pH

These are rapid corrective measures to adjust root-medium pH in pots or benches that already contain plants.

To lower pH

  • Dissolve 1 to 2.5 pounds of iron sulfate in100 gallons of water. Apply to the root medium.

To raise pH

  • Option 1
    Mix 1 pound of hydrated lime in 100 gallons of water. Allow the mixture to settle. The clear solution can be applied to the root medium.
  • Option 2
    In a plastic bucket, mix 1 pound of hydrated lime with 3 to 5 gallons of warm water. Allow the mixture to settle and pour off the clear solution into another plastic bucket. Apply the clear solution with a fertilizer injector set at 1:100 or 1:128.

Modifying electrical conductivity (salt level)

If the electrical conductivity (EC) is too high, leaching the medium with water will reduce the salt level. A corrective procedure includes a normal irrigation followed immediately by another irrigation. After this, allow the medium to dry. If further leaching is required, repeat the double irrigation. Recheck the EC level to determine whether the leaching has been successful in lowering the EC to an acceptable range. A low EC is usually indicative of inadequate fertilization. Increase the rate or frequency of fertilization.

Correcting nutrient deficiencies

Table 4
Correcting macronutrient deficiencies*

Deficient nutrient Corrective procedure and Recommended formulations oz/100 gal gm/liter

Use a high-N fertilizer.
Balance the N to K2O
calcium nitrate (15-0-0)
ammonium nitrate (34-0-0)


Use a fertilizer formulation with P equal to half or more of the N level
or use one application of diammonium phosphate
or monoammonium phosphate



Use a high K2O fertilizer formulation
20-5-30, 17-5-24, 15-11-29, 15-10-30
or use potassium nitrate to balance N to K2O


Use the N-source calcium nitrate
or use a high-calcium fertilizer
20-0-20, 21-0-20, 15-0-15, 15-5-15, 13-2-13


Apply magnesium sulfate (Epsom salt) or use a complete magnesium-containing fertilizer 13-2-13, 14-0-14, 15-15-15 17-0-17

32 2.4

Apply magnesium sulfate (Epsom salt) or use a sulfur-containing fertilizer 20-18-18, 20-18-20, 20-9-20

32 2.4
*From Nelson (1996)
Rates apply to general greenhouse crops. Lower rates may be required for lightly fertilized crops. Rates should be halved for plug seedling crops. These corrective procedures are to be applied once. Subsequent applications should be made only after a soil or foliar analysis test indicates a need. All fertilizers are to be applied as a substrate drench.

Adjustments in available nutrient levels can be made by the following additions: 2 oz of calcium nitrate (15-0-0) per cubic yard (75 g per cubic meter) to increase the nitrogen test level 10 ppm; 1 lb of concentrated superphosphate (0-46-0) per cubic yard (600 g per cubic meter) to increase the phosphorus test level 5 ppm; and 1.5 lb potassium nitrate (13-0-44) per cubic yard (55 g per cubic meter) to increase the potassium level 100 ppm.

Table 5
Correcting micronutrient deficiencies*

Micronutrient and source   Bench drench Container drench
Analysis oz/100 sq ft g/100 sq ft oz/100 gal g/100 gal
ferrous sulfate

20 percent




sodium tetraborate (borox)
boric acid

11 percent
17.5 percent




manganese sulfate

33 percent

0.25 to 0.5

7.1 to 14.2


zinc sulfate

23 percent

0.25 to 0.5

7.1 to 14.2


copper sulfate

25 percent

0.25 to 0.5

7.1 to 14.2


ammonium molybdate
sodium molybdate

54 percent
46.6 percent

*From Reed (1996) as adapted from 1981. Cornell Recommendations for Commercial Floriculture
Crops, Part 1. Cultural Practices and Production Programs.
Dissolve 1 ounce sodium or ammonium molybdate in 40 fl. oz. of water. Use 1 fl. oz. of this stock solution in each 100 gallons of final-strength fertilizer solution.
Iron, manganese, zinc, and copper are commercially available from most companies that sell micronutrient mixes as chelates of EDDHA, DTPA, HEDTA, or EDTA.

Updated 5/13/15