I got your email, Louise - Sorry, I've been away at a bonsai show & visiting friends/family. This is a tough one. As I understand it, you have a concrete block planter constructed atop a concrete slab, with no way for the water to make its way into the sand below the slab. Drilling holes in the block walls won't improve drainage. The only 2 ways to effectively improve drainage would be to make sure there is a 'bridge' between the soil in the planter and the sand below the concrete so the water can percolate through the soil, or to make sure the soil you use is porous enough that it holds little or no perched water. This would mean that your soil particles would have to be large & stable, insofar as their structure is concerned. Even the soil you see me holding above would be inappropriate for your application because that soil depends on the wicking action of the earth (in RBs) to ensure it doesn't remain saturated after rain/watering. It looks great, but if you have high standards it would be a disaster in a container or in your app. I'm thinking that about an 80% fraction of a mix of all purpose sand and all purpose gravel and 10% each of pine bark fines and Michigan (reed/sedge) peat or good compost would probably be the direction I would head. In subsequent years, I think all you'll need to do is mulch with pine bark to keep the soil healthy. If expense isn't a major consideration, you could use Turface MVP as the base ingredient for your soil. Topsoil and fine sand just isn't going to drain w/o help. The alternative would be to remove the old soil and cut a hole in the slab so water can drain from the soil in the planter, but it would have to be a hole of considerable size - preferably at the lowest point on the planter's bottom. If you have pictures, it's possible that something else might be devised that will allow the water to move out of the soil via some sort of passive wicking mechanism that we/you could devise, but I'd have to see the application in order to envision the possibilities. There might be a way to employ a false bottom by placing FRP panel on top of cement blocks that are resting on the bottom & building it like a self-watering container in reverse - where you employ a wicking column of soil to REMOVE water instead of supplying it, but I don't know how far you want to chase the issue? ;-) AL

Hi, I normally hang out on the Pool forum as that is our current main project, but as part of the redesign of the backyard we will be adding either one large 3 -4' x 16' planter. We have 2 small kids that love to plant, dig, and you know, pull the flowers out. We are planning on building these ourselves and are wondering about sinking the posts in concrete or not and how high should they be? We live in San Jose, CA, so it never really freezes here, if that helps. We will plant some flowers and vegetables like tomatoes and peppers. I have done some research on them and it seems do whatever you want is the motto. Any help in the construction, methods and materials would be very much appreciated. Thanks! Chris

Thank you @Kevin Reilly! I bought a bunch of this a while ago - think it would be ok if I mixed in some perlite? https://www.floragard.de/de-de/webshop/2037/floragard-bio-erde-lecker Peat-free organic special earth, suitable for tomatoes, zucchini, aubergines and other fruit vegetables Rich and healthy harvest thanks to the vegan fertilizer Flora Veggie Power Finely screened green waste compost contributes to the nutrient supply and invigorates the earth Safe for children, pets and animals in the garden thanks to the vegan fertilizer Coconut pulp naturally improves the water supply in the earth You can use this peat-free and vegan organic soil for all vegetable plants - whether in the greenhouse, in the bed or in the tub.

Wondering if you guys might have some suggestions for a good, long lasting barrier/membrane coat that we can use on the inside of our concrete raised planters? The outside will be stucco'ed, so we need to waterproof the walls, but are planning on growing organic veggies in them. Cheers