It All Starts With Dirt

By Janeen Feiger, Former Nursery Assistant

Here in the Garden nursery, we are frequently asked what kind of potting soils we like to use for our plants. This is not an easy question to answer since there are many factors that have to be taken into consideration: the water holding capacity, aeration, pH, potential shrinkage and more. Following are some of the components we use in the nursery with an indication of what they contribute to the mixture. You'll also find recipes for two of our most useful mixes. Please keep in mind that these mixes are what we have found work best for our uses. You may need to adjust the proportions for your particular environments and plants.

Media components

• Canadian peat: partially decomposed organic matter. It decomposes slowly and aids in aeration and drainage. It also lowers media pH.
• Sand: non-organic component of media. It provides aeration and structure to media, therefore the particle size is the critical factor in selection. Sharp sand (builders' sand) is recommended.
• Pumice: an inert material of volcanic origin. It is an excellent material for providing drainage.
• Perlite: non-organic, derived from heat-expanded volcanic rock. It increases aeration and lightens the mix without tying up nutrients.
• Sawdust: organic material providing water retention and structure. It must be composted first and should constitute no more than 25% of the mix. If a greater proportion is used, the soil will become water-logged and nitrogen deficient.
• Soil conditioner: contains processed pine bark, limestone and gypsum. This substance adds organic matter to the soil, helping retain moisture.
• Chicken grits: not an entree, but a non-organic soil amendment made of crushed granite. It serves to improve aeration.
• Dolomite: a soil amendment used to raise pH.
• Magnesium sulfate: a soil amendment and fertilizer.

Potting Mixes

The following mixes are those we use most frequently; other, more specific mixes are made based on needs of individual plants. Always determine the needs of the plant you're potting and use the components listed above to adjust the basic mixes, or create new mixes to provide an ideal environment for your plant.

• Nursery Mix: 40% Canadian peat, 30% sand, 20% cypress sawdust, 10% perlite.
• Cycad Mix: equal parts of Canadian peat, soil conditioner, pumice, and chicken grits.

Soil sanitation is essential. Media components must be free of pathogens, weed seeds and insects. Store your components and mixes off the ground so that they are protected from surface water. To protect them from wind, cover whenever they are not being used. Also, never use containers or scoops for new soil without sterilizing them first. It is inadvisable to keep soil components in storage for long periods of time. They or their bags could break down or deteriorate.

I hope this information answers some of your questions. Please remember that there is no single correct mix. There are many options available. With a little experimenting you'll be able to find what works best for you.

Copyright © 2005 Fairchild Tropical Botanic Garden, 10901 Old Cutler Road,
Coral Gables, FL 33156 USA   Phone: (305) 667-1651   Fax: (305) 661-8953