Vegetable Boxes on Concrete Deck w/ Slope?

Question

Have concrete deck on a slope (slope should be good for drainage), want two 4' by 8' boxes and I found a box 14" height. Need Advice (I'm a novice) - is this high enough? what should be on bottom of boxes? how to landscape slope? Thanks

Answer 1

Here's a comprehensive guide to creating a no-dig garden on top of concrete with the main difference being that for concrete you need to lay down some drainage in the form of twigs.

You'll need straw (and lucerne), compost, manure, newspaper or cardboard, and water. Once it's constructed the pile will build itself into a living soil to feed your plants. No need to add fertilizers.

Answer 2

14 inches is great. Perfect. You need drain holes. Nothing but sterilized potting soil in those beds. Not garden soil, no additives, don't use potting soil with water holding 'sponges or gels' and no added fertilizer IN THE potting soil. Leave at least 1" between the top of the soil and the rim.

Before planting, make sure your soil is 'lightly' compacted' to get air pockets removed. Only use plants that have been 'started'. I would not use seeds in this bed. I would create my own starts first.

Use a simple balanced fertilizer such as Osmocote 14-14-14...once per season. Extended release should last the season. Where do you live? Sub tropical? Well, that would mean twice per year.

I am not sure what your slope looks like, the percentage, is this OFF the concrete? Where does water go when it rains? This is kinda my field, grading and drainage. Send a picture of what you've got going. What are you using for the raised beds in terms of structure. Do not use compost or anything that hasn't been sterilized in the soil. I can explain in detail. And next big question is what you are thinking of planting. Annuals, perennials, shrubs, vines...trees? A combination? We can help with watering practices. Try to incorporate plants that thrive with the same environmental conditions. Don't use tropical plants with succulents for instance.