Top Soil How deep.???

[Fr_303]

Happy New Year all the best for 2008 to all!!!

I just finished my retaining wall project and I'm now ready to fill it with some small plants. The Garden bed measures 16.2 x .4 meters, How deep should I go with the top soil????. The fill currently is a clay soil, and I was going to use that mushroom compost topsoil.

Also The retaining wall is bricked and i was going to seal it with bitimun paint before i but the soil in, Do I have to seal it?? and if I do will the paint be enough??

[Jacksin]

I think around 300mm would be deep enough for plants, perhaps even first digging in a layer of gypsum to break down the clay to assist with drainage.

From my experience with mushroom compost I find it gradually breaks down and disapates having to be replaced after a couple of years so I think you would be better filling the area with sandy loam and topping the last 100mm with mushroom compost (if you really want) or even a thinner layer of mulch.

Other far more learned members will assist you with the wall.

[Timed Out]

Jacksin's on the money with digging in gypsum. If you don't break up the clay base you might run into drainage problems. Also your plants may struggle if/when their roots hit the clay subsoil.

When I did my retaining wall I incorporated gypsum, backfilled with an organic loam then put a layer of mulch on top. The plants are thriving.

Sandy loam in garden beds can be a bit too free draining unless the plants require a loose mix (e.g. succulents, cacti, lawn etc.).

One word of warning with mushroom compost - it can be very alkaline. If you're thinking of putting in any acid loving plants in the bed (e.g. camelias, azaleas, gardenias) I would advise against using it as a mulch or soil improver. A good organic compost would be a better option.