Companion planting is the practice of interplanting two or more plant species where at least one provides benefits to the other(s). Ideally, each species in any given group belongs to a different plant family and provides benefits to all the others.
To grow a monoculture is to grow a single species of plant. A polyculture is the opposite of this and is the practice of growing different species of plants all mixed together in the one growing space. Companion planting is a special type of polyculture, where each species in a garden bed or container is chosen because of how it interacts with the other species that have been selected. Ideally, a garden bed that has been planted using companion planting techniques will contain a mix of plants from different plant families that are all different heights and which provide various benefits to the surrounding plants.
What companion planting can accomplish
When practised correctly, companion planting can provide a wide range of benefits for your garden. For instance, companion planting can:
- Protect your plants from garden pests
- Prevent plant diseases
- Control weeds
- Reduce or even eliminate the need for pesticides
- Save you money on fertiliser
- Maximise your use of whatever space you have available for gardening
- Help you grow a garden that is more attractive
- Improve your harvest
- Help your plants to grow better
How to practice companion planting
The simplest way to practice companion planting is to mix a range of plant species in any given growing space. A slightly more strategic way to do it is to select plants from different plant families and mix those together.
The best way to practice companion planting is to choose plants that you know provide benefits to each other. How do you know that? There are two ways.
The common way — companion planting lists
The internet is full of companion planting lists. A quick google will net you pages of lists for good companions and bad companions. For instance ‘basil loves tomato’ is a common companion planting example.
This approach can be useful, especially if you develop your own lists based on careful observation of combinations you try yourself. Be aware though that not all companions are universal. As an example, basil and tomato don’t always go well together. In humid climates, basil grown under tomatoes may get black spot or other fungal diseases.
Some oft-celebrated companion planting ‘wisdom’ is also just ‘wives’ tales’ or not the full story. To take the example of basil and tomatoes again, experiments have shown that basil doesn’t improve the flavour of nearby tomatoes. Basil can repel a specific species of root-knot nematode, though other companions are more effective. And scientific research has shown that basil can increase tomato yields by 20% but only when basil plants significantly outnumber tomato plants. When grown in reasonable proportions, basil doesn’t seem to increase tomato yields.
So, if you want to use companion planting lists to help you practice companion planting, seek out reliable information. If possible, use information that is backed by rigorous research. And, as you experiment with companion plants, record your observations so you know what works in your unique conditions.
The best way — companion planting principles
When you look at the available body of legitimate companion plant lists, there isn’t a huge amount of information. When you rule out lists that don’t work in your area, the list becomes even smaller. As a result, the best way to get started with companion planting is to use tried and tested companion planting principles and incorporate specific companions when available and as needed.
Once you know the principles of companion planting, you can quickly develop companion planting habits that work even when you don’t know which companions work best together. As an example, aromatic plants protect their neighbours from pests so you could choose to include at least one type of aromatic plant in each of your garden beds.
Following the general principles of companion planting will enable you to create a robust garden that will weather adverse conditions and resist pests and diseases, even when new ones arrive. You can then use specific companions to combat specific issues when they arise or when they offer a specific benefit.
As an example, I follow the general companion planting principles but I always plant broad beans amongst my potatoes to prevent fusarium wilt. While I’ve never (touch wood) had a garden succumb to fusarium wilt, the risk of not being able to grow susceptible plants, like potatoes and tomatoes, for many years after an infection prompts me to take all possible precautions.
Where to source companion planting information
You can find scientific studies on companion planting by doing a search in Google Scholar.
I’m in the process of finalising a new book on companion planting that details all the companion planting principles. If you’d like to be notified when it’s released or get an advance reader copy, sign up for my mailing list below.
If you garden in Australia, I’ve produced a companion planting book that covers the companion planting principles and includes lists of plants that are known to work in Australian conditions and against Australian pests and diseases.
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