Q Could you give me a recipe for an all-purpose potting mix that will last about four years or more without deteriorating? I will adjust the size of the material according to the root size of the plants. What do you think of a recipe consisting of 50 percent redwood bark and 50 percent Grodan Rockwool (80 percent absorbent:20 percent repellent for phalaenopsis, and 60 percent absorbent:40 percent repellent for cattleyas and dendrobiums)?

A I regret to inform you that it is difficult to find any potting material with a four-year life. The mix you describe would come close, but only with a repotting at two years, retaining the old rootball. The Europeans do not seem to mix the rockwool with any biodegradable material, so maybe the redwood would cause problems. I believe it is wise to have all your plants in the same mix for ease of watering. If it is bark, this may mean coarse bark for bigger plants and finer bark for smaller ones. But the fertilizing schedules can then be standardized. I like your 1.5:1.0 ratio of absorbent and water-repellent rockwool for the cattleyas, dendrobiums and phalaenopsis, which would be content with this mix indoors. However, you might find a 3:1 ratio better for outdoor growing under shade cloth. — Andy Easton.