Hi there I’m in the process of designing a slab base for a redwood forest and thinking off using fiber glass to make a large slab with a slope from one side down and main question what soil mix would you use as redwoods need a lot of water retention would you use a straight Akadama
Anyone ever used fiberglass for a forest planting ?
I have no direct experience with either but based upon related experience here are my comments.
Make sure the slab is really nice and stiff to avoid flexing and root disturbance. One approach is to use some steel reinforcing bar in underneath to build and basic structure and then fine wire mesh to create the shape. I have used rigid foam insulation to create the shape and then covered with layers of epoxy-fiberglass. Lighter weight fabric is easier to shape, but requires more layers. I would use a 5-6 oz/sq yd (160 - 200 g/m^2) satin weave so it drapes fairly well. If you leave the foam in place I would plan on about 6 layers on the top and sides with 2 or 3 underneath. If you choose to remove the foam (acetone will dissolve any remaining after you dig most of it out) then I would plan on about 10 layers with 4-5 on the bottom. Two notes: 1) Polyester resin will dissolve the foam and is rather nasty so I recommend the more expensive epoxy. Make sure to wear appropriate PPE to protect yourself from both dust while sculpting the foam and the epoxy while applying the cloth. The correct ratio of epoxy is about 50/50 by weight, but this type of layup will generally be resin rich.
I am developing some redwood seedlings and they are growing in a mix of screened bark and pumice. I grow my deciduous bonsai in 75% akadama and 25% pumice and would use that or a 50/50 mix for redwoods if you are in a wet climate. I like the structure the pumice provides and helps prevent the soil from becoming water logged.