The PGC Primer offers a brief introduction to the various topics that impact users. It includes reccommendations developed by PGC users over the years.

Growing Media

There are three standard growing media available for PGC users. Custom mixing of growing media is available, please discuss your requirements with the PGC manager.

MSU Mix (test results, September 2015)

Mineral soil, Canadian Sphagnum peat moss and washed concrete sand are blended on a 1:1:1 by volume ratio. The wetting agent, Aqua-Gro 2000G is added to the mix at the rate of one pound per cubic yard. This additive allows for easier initial watering of the mix. MSU mix is aerated steam pasteurized using the Lindig soil treatment system for one hour at 70C.

Soil test results (July, 2004) for MSU mix show a pH of 6.1 and EC of 0.9 dS/m. Test results will vary as the mineral soil component is purchased from a private vendor and is often a composite of various soils found in the Gallatin valley.

Sunshine Mix #1 (test results, September 2015)

This commercially available soil-less mix is a blend of Canadian Sphagnum peat moss and horticultural grade Perlite. Sunshine Mix #1 is buffered with Dolomitic lime and contains a starter fertilizer charge and wetting agent. Test results (July, 2004) show a pH of 5.9 and EC of 1.1 dS/m.

50:50 Mix

50:50 Mix comprises of half MSU Mix and half Sunshine #1 by volume. This mix is offered for users desiring a mix with a lower bulk density than MSU mix, but retaining a mineral soil component. 50:50 mix doesn't shrink in the container when dry as much as straight Sunshine Mix #1.

Media Selection Guidelines

Your selection of a growing media largely depends on container size and the desirability of a mineral soil component in the media. Sunshine Mix #1 is the best choice when growing in shallow flats, plug trays, small pots (6" and smaller) and 1020 flat inserts (i.e. six packs). Your plants will benefit from the greater porosity of the Sunshine Mix #1 in these styles of containers.

Use MSU Mix when a mineral soil component is desired. MSU mix performs best in 6" and larger pots. Over time MSU Mix's pH will rise over time more so than Sunshine Mix. If your plants require slightly acidic media conditions, and you are growing in MSU mix, you will need to pay close attention to pour-through test results and make the appropriate fertilizer selection to maintain desired media pH levels. Details on the pour through test and fertilizer selection are covered in the Water Quality and Fertilization section below.

Water Quality and Fertilization


Water Quality

The PGC water source is from the City of Bozeman 's water treatment plant. The most important parameter of water quality is the alkalinity rating. Alkalinity is the measure of a water's ability to raise growing media pH. The PGC water is in the 100 mg/l CaCO3 range, which is a moderate level of alkalinity. The impact on users is that our water will slowly cause your media pH to raise over time. To counteract this tendency you should select a fertilizer that has a moderate to high level of potential acidity. The PGC office has pH and EC (soluble salts) meters for use. The pH and buffering capacity of the growing media also impacts your fertilizer selection. Some recommended starting points follow.

Fertilizer Recommendations

All high quality greenhouse fertilizer labels have the following information:

  • A three number code that list the amount of nitrogen, phosphoric acid, and potash (N-P-K)
  • A listing of secondary and trace elements
  • Sources of elements - Especially important is the ratio of ammonium nitrogen (acid forming) and nitrate nitrogen (basic)
  • Rate and frequency of application information
  • Fertilizer solution electrical conductivity table - Allows users to check the function of their fertilizer injectors

Sunshine Mix #1 Users

This peat based media has a pH of 5.9 and requires a fertilizer with moderate potential acidity. A 20-10-10 formulation would be a good starting fertilizer. Pour-through test results performed during the cropping cycle might indicate a need to change formulation to adjust media pH.

MSU Soil Mix Users

This soil based formula has a pH of 6.1, but does not have the buffering capacity of Sunshine Mix #1. Users might consider using a 20-20-20 formulation of fertilizer which has a high potential acidity.

Fertilizer Delivery

The most common method of applying fertilizer is injecting it into the irrigation water.  The PGC will provide you with a "Hozon" bucket injector with a injection ratio of 1:16.  This means you must make a stock solution that is 16 times stronger that the required fertilizer concentration.  The injector is screwed onto the hose bib and the black tubing is placed into your stock solution.  As water passes through the injector it creates a vent uri effect and siphons fertilizer into the water stream.