How Do You Prepare Soil For A Roof Garden?

Young women mixing soil and compost in a rooftop community garden, How Do You Prepare Soil For A Roof Garden?If you don't have a lawn to work with, growing produce at home can be a little difficult. You do have options, though. So long as you have your work approved by your landlord or other appropriate authority, you can start a rooftop garden. How, though, do you go about preparing soil for a roof-based garden?

You can't use normal soil for rooftop gardens, or else you put the longevity of your produce at risk. Instead, you'll need to fix together the following garden additives:

  • Peat moss
  • Compost
  • Vermiculite

Once you have these additives prepared, you'll just need to find a container, mix them together, and start planting!

Do you feel up to the challenge of mixing your own soil? Here we'll give you the tools you need to prepare your roof for a rooftop garden and how to mix your soil for ideal growth. Just keep reading!

Preparing Soil For Rooftop Garden

More often than not, the type of soil you use for your rooftop garden will vary based on the produce you want to grow. If you want an ornamental garden as opposed to a utilitarian one, you'll want to take the needs of your flowers into account when mixing your soil, fertilizer, and additives.

In general, you'll want to prepare your rooftop for its soil layer with all of the following:

A Waterproofing Layer

Before you start laying soil, you'll need to ensure that your roof has been waterproofed and frost-proofed. Even if you're growing your garden in separate containers, waterproofing your roof with either a liquid waterproofer or tarp will protect your home from spill-over.

An Insulating Layer

The insulating layer beneath your soil will help your amalgamation stay moist, even in the worst of the summer. More often than not, you can re-purpose XPS extruded polystyrene boards and lay them above your roof to better protect your garden.

A Layer For Drainage

If you want to keep your produce's roots from rotting, you're going to need a drainage layer to draw excess water away from your plants. This layer can take the form of a tarp, marbles, or other water-resistant materials.

Geotextile Fabric

The geotextile layer between your soil and the drainage layer will keep your soil from spilling out with the excess water. These layers should be waterproof and dense enough to support your soil but not so dense that they won't let water through.

A Layer For Vegetation

Finally, it's time to lay down your soil. You'll be able to determine how much you need based on the stated needs of your produce. If you're planting potatoes, for example, you'll need to have enough of your soil mixture on hand to create mounds when the potatoes need to be buried.

What Materials Do You Need For A Rooftop Garden?

With the aforementioned necessities in mind, what materials do you need to create a welcoming soil for your plants? 

Peat Moss

Peat moss consists of dead moss and decomposing materials. It works similarly to compost, providing your garden with extra nutrients that it might not get naturally. Peat moss will also help your soil mixture retain its moisture, whether or not you've watered recently.

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Light Compost Soil

Light compost soil consists of decomposing old plants, a little bit of natural soil, and the waste from earthworms. This amalgamation of natural resources lets your new garden take from the gardens of old, reusing nutrients that have gone in and out of someone else's kitchen.

When you use this kind of compost, you'll be giving your garden a boost and ensuring that it has the nutritional base to remain healthy through its growing season. 

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Vermiculite is similar in composition to fertilizer, though the two are not interchangeable. You'll want vermiculite in your rooftop garden because it serves as a soil substitute. When it works in combination with the aforementioned peat moss and compost, it'll help your produce grow, regardless of the composition of the soil in your area.

It's the air to water ratio in vermiculite, too, that helps your produce grow a little faster than it would otherwise. 

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Bringing Your Soil Additives Together

Once you've procured all of your necessary ingredients, it's time to mix together the perfect soil for your rooftop garden. To get started, all you need to do is:

  1. Place your peat moss, compost, and vermiculite in your container of choice.
  2. Mix the additives together until well-combined. You can do this with your hands or with a gardening fork.
  3. Plant your growths or seeds an appropriate distance apart.

Why Can't You Use Real Soil In A Rooftop Garden?


You might think that the aforementioned mixture seems a bit unnecessarily complex. After all, can't you make a rooftop garden by plopping dirt into a container along with some seeds?

In theory, yes. In practice, no.

To start a rooftop garden, your soil needs to meet a number of requirements set forth by your city and by whoever owns the building you're in. This soil not only needs to have a controlled pH, but it needs to have no negative impact on the roof and on the people that roof protects.

That's not the only reason, though, that you need to carefully cultivate the soil for your rooftop garden. If you opt to use dirt from around your city without any additives, you'll find yourself dealing with soil compression sooner than you will a successful harvest.

Young women mixing soil and compost in a rooftop community garden, How Do You Prepare Soil For A Roof Garden?

Peat moss and vermiculite let air circulate through your garden which makes it easier for your plants to thrive. Without this airflow, the roots of your plants will suffer from excessive pressure, and your harvest will fail.

Can You Grow A Rooftop Garden Without Soil?

If combining different garden additives doesn't sound like your cup of tea but you still want to grow a rooftop garden, you can always start a hydroponic garden. You'll need to have this rooftop garden approved by your landlord or appropriate authority. Once you have, though, you'll be able to forgo artificial soil mediums in favor of nutrient-rich water.

How Do You Water A Rooftop Garden?

Watering a rooftop garden isn't too different from watering a ground-based garden. You'll want to vary the amount of water you use on each of your containers based on the needs of your individual produce. Make sure, though, that you've firmly established your rooftop garden's waterproofing layer and drainage tarps. Without these, you not only risk drowning your garden, but you risk damaging your roof.

In general, try to keep the soil in your rooftop garden moist. If it's rained recently, go up and check the consistency of the soil before watering again. Remember, though: the needs of each garden are different. Research what your produce prefers before committing to a watering plan.

In Closing

Are you ready to put your green thumb to the test? Get your garden approved by your local authorities, and you'll be able to start mixing your soil substitutes together. 

Be sure to check out this other rooftop gardening guide: What Are The Common Problems With Rooftop Gardens?

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