Answer: A typical rule of thumb is that the plant's root system will be as large as its top growth of branches. If the root system is overly restricted then the top growth will eventually become stunted and the plant may die. This concept is taken to an extreme in the art of bonsai gardening where plants are literally dwarfed by growing them in miniature pots.
Apache is considered a "dwarf" form of pyracantha and is recommended for (large) containers and smaller spaces, so it would be one of the better choices of pyracantha for a location where space is an issue. It does however reach a mature size of about four and a half feet tall and over six feet wide, so it is not actually a small plant. A limited soil area will probably necessitate regular watering and the top may need to be pruned regularly to keep it in balance with the root space. You may find the National Arboretum's description of the plant at
helpful. Your local county extension and nursery personnel may also be able to help you determine if this particular plant is the best choice for the location you have in mind.
I hope this answers your question.
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