Creating Your Growing Media
The foundation of a successful balcony garden is the growing media you use. In this post, I’ll walk through my recipe for a balcony growing substrate.
West Broadway, New York, Piet Oudolf
Finding a durable and lightweight potting mix suitable for long-term use can be challenging for non-commercial gardeners. Many off-the-shelf potting mixes degrade over time, losing their beneficial properties and becoming overly heavy, which could risk exceeding the load capacity of your rooftop.
To address these issues, I've developed a custom recipe designed to ensure the long-term health of potted gardens. This mix not only supports sustained plant growth but also helps manage the weight constraints of rooftop & balcony gardening. You will need to source the individual ingredients and mix them yourself.
The growing media should be made of a mixture of the following ingredients:
Biochar (5%)
Adds to the mix's ability to retain nutrients and water, and its porous nature supports microbial life, which can enhance soil health.
Supplier: Purchase online. As this is a small percentage of the overall mix, I recommend just ordering this in bagged form online.
Premium Potting Mix (20%)
Provides essential organic matter and nutrients, supporting plant growth. The low percentage helps in preventing the mix from compacting and breaking down over time, which is great for maintaining structure. Can be supplemented with an annual
Supplier: Any Garden Centre
Vermiculite (25%)
Excellent for moisture retention and aeration. It will help keep the mix light and ensure good drainage, preventing waterlogging, which is crucial for balcony plants that can be subject to variable weather conditions.
Supplier: Goat Hydroponics in Mitchell (100L bags) or for smaller quantities can be bought from hardware stores or online
Recycled Crushed Brick 14mm (50%)
A fantastic choice for promoting drainage and aeration while adding bulk to the mix without being too heavy. It’s an eco-friendly option as a recycled material.
Supplier: Canberra construction recyclers
Estimated Weight: Between 866 kg/m³ and 1120 kg/m³.
This combination should provide a stable, well-draining, and nutrient-retaining growing environment for your balcony plants. It balances the need for water and nutrient retention with sufficient drainage and aeration, which are critical in a container setting. Just make sure that the crushed brick is free of any substances that might be harmful to plants. Also, monitor how your plants respond to the mix, as you might need to adjust the ratios or add specific nutrients depending on the types of plants you are growing.
Note:
I recommend once you’ve created your growing media, mixing together the ingredients thoroughly, do a pH test on it to check it’s pH. It may be alkaline and need some sulphur added to the mix to lower the pH. The ideal range is 6-6.5, 7 at most alkaline.
Most of the assumptions made while estimating the weight and functions for this growing mix used information published in the “Growing Green Guide: A guide to green roofs, walls and facades in Melbourne and Victoria, Australia” published by the University of Melbourne.
You’ll need to verify the weight yourself - this is a broad guide to send you in the right direction but weight differences in individual products or different ratios for your mix can result in a heavier media.
Platinum house by Sydney based landscape company Secret Gardens
Creating the right growing media is crucial to your garden’s success. If you need help sourcing materials or setting up your garden, get in touch for personalized advice and installation services.
Want to keep reading?
Check out the next post in this series: Drainage, Watering & Nutrient Delivery.
Want expert help?
Check out my Balcony Design and Construction Services page.
