If you have been growing orchids for any length of time, you know how easy it is to run out of space for your ever-expanding collection. Orchids are a bit like peanuts or potato chips, you can't stop with just one! If you are growing on a window sill, you have the option of expanding to more windowsills within your house, or if you are lucky and have the space, to an outdoor greenhouse.
No matter which way you grow, you are going to need to increase the density of orchids within that space as your collection grows. Be sure that you have an active pest monitoring schedule whenever you try to increase the number of orchids because the closer together they are, the easier it is for pests to move between plants. Another good thing about increasing density is that the humidity around your plants will also increase, making your plants happier and healthier. Here are some good ideas to accomplish that.
Small mounted plants can be hung on the side of existing pots of larger plants. Tolumnias are a good choice for this because the plants stay small and do not require large mounts. You will want to move them when they are flowering in order to display the flowers to best effect.
Layering plants by hanging high light plants above those that require lower light levels is another option. Plants can be hung either in baskets or in pots. Put your high-light loving plants such as Cattleyas, Vandas and Dendrobiums at the top of your growing area; then the medium light plants in middle layers and finally the low light plants such as Paphs and Phals on the bottom layer shaded by the others.
If you have a greenhouse, one of the best ideas I've seen is to tack a piece of fencing with fairly large openings to one side of the structure. This can be used to hold many mounted plants of almost any size. If you use very sturdy fencing material, you can also attach pots to the material. Use the same idea that we discussed above -- high light plants on the wall -- to shade the lower light plants. You can also use this idea to provide some cooling for a warm greenhouse if you use the west wall as your mounting area -- it will provide shade against a strong westerly sun.