Rooftop Garden Liners and Soil

If you live in an apartment, or have a flat roofed home, a rooftop garden is a great way to reduce your carbon footprint and introduce your family to the joys of horticulture. You can start with a ready-to-use liner, or build your own rooftop garden, just be sure that you use the right kind of soil, and provide for adequate drainage.

Types of Garden Liners

Major hardware stores carry one-piece garden liners that can be filled with soil and are ready to go. If you want to make your own, build a frame or box, and use heavy polyurethane or rolled plastic, or purchase an above-ground pool liner. You could start small with one or two planter boxes, and build the rooftop garden slowly, adding new sections as previous ones have been planted and are doing well.

Simple Rooftop Garden Designs

When creating your own rooftop garden, you can incorporate variations in the design. Build a step design to have access to  plants of different sizes. With separate liners, you can also provide different soil and moisture requirements, such as very light, loamy soil for roots and tubers, and stronger, more supportive soil for plants such as corn or okra.

Rooftop Garden Drains

Be sure to provide a way to remove excess water from a rooftop garden liner.

  • If you are using a wooden frame, glue a 3 inch square of the liner to wood, and then drill a hole large enough to insert a small piece of PVC.
  • Connect a hose to the other end of the PVC, and drain it down to ground level.
  • Avoid draining directly onto the roof, as it may result in puddling, or excessive roofing erosion. Even a small drip can be quite destructive.

Rock, Sand and Soil

A solid rooftop liner should be deep enough to place three layers of material.

  • At the very bottom, about 2 inches of crushed stone or pebbles allow water to filter out of the soil and drain away.
  • Above that, add 4 to 6 inches of sifted compost and coarse sand, mixed in equal parts.
  • For taller plants, use 1/2 sand and 1/2 clay. Over the top of your growing soil, 2 to 3 inches of mulch can be used to control weeds and help protect the planting soil.

Weight Distribution

Be careful that you do not add more weight to the roof than it is able to support. When building frames, always use a solid bottom rail along the rooftop that distributes the weight more evenly across the whole surface. If you do not distribute the weight properly, your roof may leak or even collapse.

Impromptu Gardening

Buckets and flower pots can be used as immediate gardening containers for the rooftop. One common example is to sow radish seeds in a simple window planter or flower box, but you can also place a trellis in a 5 gallon bucket and grow beans, squash, and cucumbers. Save your coffee and tea grounds, and use them to add nutrients to plants soil.