Soil-Mix Ratios & Growing on Patio or Roof

Artificial soil mix and Grow-Boxes on a patio or flat roof


1) Are the percentages of the components in artificial soil by weight or volume?

2) Are there rankings of which materials are better?

3) Can I use normal sand instead of fine sand?

4) I want Grow-Boxes on my balcony. Will this work with no real soil beneath my Grow-Box?

5) What about drainage?



1) Soil mix percentages are figured by volume, and sand should be between 25% and 35%.

2) The best soil mix alternatives are generally whichever are the least expensive. Sawdust lasts longer than peatmoss, and perlite lasts longer than vermiculite, but sawdust takes some nitrogen while it is fresh (rarely enough to be a problem, if you are feeding properly), and vermiculite is preferred by some growers over perlite because of the smaller particles. Also consider rice hulls and ground coconut husks, which may be available in many places.

3) Extremely fine sand isn’t the best, but you don’t want anything too coarse. It should be clean (no seeds, bugs, diseases, or dirt). In the USA we request “concrete sand”.

4) We have pictures of excellent gardens on asphalt parking lots, on patios, and even on roof-tops. Remember that 95% of the plants’ needs come from the sun and air, along with water. You should drill many holes for drainage. Lack of drainage will kill your plants faster than almost anything else.