We have a large and very old rhododendron and want to remove it and put a greenhouse on the site. We understand that the roots are probably very deep and far-reaching, but a professional gardener friend has said that if we get out as much of the root as possible and then check regularly all around the greenhouse for re-growth it will not be a problem to zap the growth with Roundup or similar. The person who is going to do the work says he will grind out as much of the stump as he can. Should we lay the greenhouse on concrete (not recommended by another gardener friend) or railway sleepers (recommended), and can we expect the Rhododendron roots to eventually lift the greenhouse off its moorings!
The greenhouse is probably best set on a row of concrete blocks on a 150 to 200mm foundation of concrete. In this way you can have access to the open soil within the greenhouse which is much better for growing.