Greenhouse Gardening

Growing Media

Soil found outside stores and releases nutrients, provides plant support, and creates passages for air and water. It contains living things—bacteria, mites, and worms, as well as nonliving substances—small particles of sand and clay. Greenhouse soils need to be lighter than garden soils, because frequent watering tends to pack soil down. Many greenhouse growers use soil-based or soilless mixes that have been heat-sterilized so they contain no living organisms such as fungi, weed seeds, or insects that thrive in an inviting greenhouse environment.

Mixed Media

Mixes for Containers

We recommend using a commercial soilless mix (available at garden centers, nurseries, and hardware stores) for starting seedlings, which are particularly susceptible to disease and require a light medium that holds moisture well.

If you and your students are adventurous, you can make a soilless medium yourselves:

Soilless Recipe

Mix in equal parts:

• Canadian peat moss
• perlite
• vermiculite

Although good for starting seeds, these soilless mixes are low on nutrients and tend to dry out quickly. For larger plants, you should find a heavier commercial potting soil that contains some sterilized soil or organic material.

Mixes for Beds

If you're growing in beds, it's best to provide a soil mix that closely approximates soil found outdoors. If your outdoor soil is heavy, you'll need to improve its drainage for use in the greenhouse. Adding compost, peat, or other organic matter to the soil helps with this balancing act.

Soil for Beds Recipe

Mix in equal parts:

• rich soil
• organic material (peat moss, leaf mold, or screened compost)
• drainage material (sand, vermiculite, perlite)

You'll also need to check and adjust the pH (to keep it between 6.0 and 6.8) and may want to add other mineral amendments (e.g., bone meal) to provide additional nutrients.

When filling beds, first lay down a few inches of gravel and a few inches of sand on the bottom for drainage, then add 1 1/2 feet or more of your soil mix.

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