This page shows photos of growing media used in cultivation of bulbs.
Bark can be used for growing geophytes such as Oxalis. However, certain types of bark such as the orchid bark below can be rather expensive. The photo below by Nhu Nguyen shows two sizes of orchid bark.
Coir is a product made from the husk of coconut fruits. Grounded products resemble peat moss but there are a few differences. One major difference is that coir holds on to water very well and is not recommended for plastic pots in cool and wet places. Geophytes in terracotta pots in warm and dry places can be grown successfully using coir. Some growers avoid using this product while others have good results. If you decide to use coir, it is only good as part of a mix and all raw coir products should be washed at least once to remove salts (3x is best). Most growers that use coir suggest that the product be buffered with calcium sulfate (gypsum) and magnesium sulfate (Epsom salt) before use.
Peat moss comes from peat bogs where sphagnum moss die and compress over thousands of years. It is a light and fluffy material that is low in pH. Use of peat moss is not recommended these days since it is environmentally unfriendly due to unsustainable harvesting and bog habitat destruction.
Perlite is like poprock (equivalent of popcorn). It is made from hydrated obsidian. When heated to 850–900 °C, water trapped inside the material expands and leaves all the great pores in the rock when it cools. It is a versatile substance, lightweight and holds water well. However, because of the lightweight, it tends to float in the pot when watered and heavy rain can wash the floating particles away. Some people also find the white perlite dust rather annoying to breathe in. It is available in several sizes. The photo below by Nhu Nguyen shows a smaller sized perlite.
Pumice is a magical substance for growing geophytes. It is expanded volcanic rock which is formed naturally and is mined out of the earth. When used as a growing medium, it provides excellent drainage, holds just enough water, and dries out much quicker than other material. When dried, pumice particles change color making it easy to know when to water. For certain difficult to grow geophytes such as Worsleya, this material makes all the difference. I grow desert bulbs in pumice with 10-30% organic material in terracotta pots. The combination of this great material and the breathable terracotta works wonders in my rainy climate. It is often sold in bulk in feed stores under the name Dry-Stall (not to be confused with Stall-Dry). The photo below by Nhu Nguyen shows both dry (lighter) and moist particles (darker).
Sphagnum moss is a bog moss which is excellent for holding water. It is available in long and short-fibered. Long fibered tend to be more expensive. New Zealand sphagnum is sustainably harvested. The photo below by Nhu Nguyen shows New Zealand long-fibered sphagnum.
Sand is often added to medium to provide drainage. There are many types and sizes.
Vermiculite is made from expanded basaltic material. It comes in several sizes and can look quite different but the identifying characteristic is that they all flake as apparent in the larger particles in the photo below. It holds water well, but tend to stick to everything and will compress after being in a pot for a while. The photo below by Nhu Nguyen shows a smaller sized vermiculite.
