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Companion Planting


A concise definition of companion planting is where two or more plants grow in symbiotic (harmonious) relationship. Correctly grouping plants requires planning and good research. To learn and understand their unique characteristics helps to create a beautiful healthy garden for all to admire. As gardeners our reasons to companion vary.

Our effort to produce stunning blooms, rehabilitating poor soil, attract beneficial insects and pollinators is most rewarding irrespective where we live and land size available to us. I have always found companion planting to be my first gardening method due to its success over many years.

Plants are intelligent. They know how to extract nutrients deep in the ground to make available for the plant’s survival. Photosynthesis supports the process.

The many unseen critters working industriously below our feet – microbes, insects, worms, mycorrhizal fungi, and beneficial soil bacteria create beautiful humus for good plant health. In return, they flourish and fruit for our enjoyment and harvest. This can only be achieved when giving plants the ideal spot to grow and good feed. A good example of what not to do is plant shade loving Daphne odora in full sun or Oregano vulgare underneath gum trees.

Often, we fall in love with ‘I have to buy that plant’ without proper research. The outcome is often disappointing. We have done our money feeling disappointed the plant has not performed as we expected. Companion planting is not an old-fashioned concept. It is incredibly simple if you follow a few horticultural guidelines. Companion planting is often implemented among biodynamic, organic and permaculture practices. If you are not a confident gardener, start with a small area and a few plants; note your observations.

Companion planting extends beyond growing garlic and lettuce together. There are horticultural complexities and many elements to consider. Learning this method encourages the gardener to understand how plants function in their environment, and why they require correct growing and feeding conditions to flourish. This method is suitable for courtyards and small spaces using fixed position or moveable pots.

Listed are a few combinations:
Potato and lettuce, radishes, spring onions, strawberries, celery. Companion marigolds to ward off pests, peas to provide nitrogen.
Apricot and dill, parsnips, anise, carrot. Underplant with white clover, buckwheat to attract predatory insects. Avoid planting near plums, strawberries or solanaceae plants. Apricot susceptible to fungal and verticillium wilt.
Borecole (collard greens, broccoli, kale) with dill, mint, sage, rosemary suggests an improved borecole flavour. Companion with late cabbage or potatoes. Avoid strawberries, tomatoes.
Tip: learn the plant’s botanical name to properly identify; common names can be misleading.

Soil Health and Allelopathy
Allelopathy is when plants release toxins to discourage nearby plant growth either positively or negatively. An example is planting underneath gum trees.
Overall, we want to achieve healthy soil, good yield, and attract beneficial insects. Remember there are no perfect combinations. The below mentioned guidelines kickstart the process, experiment and have fun.

To get you started, here are some questions and pointers breaking down the process:
Why do I want to create a companion plant garden? Steep slope, combat soil erosion?
Do I want to create an aesthetic landscape? Wildflower prairie?
Organically nourish soil to create a healthier microbial environment?
Low or high maintenance garden?
I want to increase yields, soil biology and chemistry.
Deter pests? Attract beneficial insects? (Consider interplanting.)
Create a low allergen, native bushfood garden?
What aspect (direction) is the garden bed facing?
Does that area receive sufficient light? Airflow?
What plants including trees exist on my property?
Are seasons problematic? (Wind, rain, extreme heat.)
Soil type – clay, sandy loam, clay loam etc., alkaline, acidic?
Am I in a bushfire zone?
Wetland environment?
Suppress weeds? (Remember not all weeds are bad, some are sadly given a bad reputation.)
Consider plant cycle – annual, biennial, perennial.

Property infrastructure
Where is my infrastructure located? It is crucial to know exact location of gas, phone, water, sewerage, and power, the “she’ll be right attitude” is dangerous. If unsure have a qualified tradesperson check for underground utilities. Dial before you dig is a good place to start. For many on rural / semi-rural and potential new home buyers to purchase these types of properties you must KNOW exact locations of septic tank and effluent lines. Septic specialists offer information where to avoid planting around these systems. When you think about it, would you consume food grown from untreated human effluence? Planting shrubs or trees too close to pipes give roots an excellent opportunity to seek food and may infiltrate pipes causing them to break discharging untreated sewerage. Not a pleasing situation for the homeowner and never underestimate a plant’s root system.

Here is a personal experience I will share with you about root systems. At our previous home we had a beautiful twenty year plus Japanese maple in our front yard. After some heavy rains I heard water trickling inside the lounge room wall. I went outside to investigate pulling up one of the downpipes and was horrified to see the Japanese maple roots growing upwards inside the downpipe. We called out a plumber to investigate and clean out any blocked pipes. He removed metres of matted roots, brought in the excavator to remove, and lay new pipes. Unknown to us, the tree had crushed terracotta pipes causing vast damage.

By now you should be confident to start out.

Allelopathy – antagonistic by repelling nearby plants.
Aspects – north, south, east, and west.
Deciduous – plants drop their leaves annually and new growth re-emerges in spring.
Evergreen – plants hold onto their leaves greening all year round.
Genus – plant category.
Herbaceous – fleshy, soft stems, non woody plants.
Interplanting – growing two or more crops in the same place at the same time, good use of space.
Mycorrhizal fungi – a symbiotic association between a green plant and a fungus (Wikipedia).
Photosynthesis – a process used by plants using sunlight to synthesize nutrients from carbon dioxide and water releasing oxygen. The green leaf colour is called chlorophyll.
Plant cycle – annual (grows, dies back setting seed in one cycle), biennial (plant cycle of two years – grows, set seed, and dies back), perennial (lives more than two years).
Semi deciduous – plants that lose leaves for a short time.
Symbiotic – where two or more species live in harmony.
Trap plants – plants specifically chosen to attract pests detouring from good crops.

Companion planting charts (mostly based on northern hemisphere observations)
CFA Victoria website – how to prepare your property and plant selection key
Council and Landcare publications
TM Organics – Tim Marshall (Australian) books
United Nations Soil publications

About the author
As a child Diana always loved nature – plants, medicinal herbs, animals, and anything connected to the natural world.

Over the years she consistently wrote garden articles and presented plant topics to various garden clubs and worked in different areas of the industry.

Diana completed a full time Diploma of Horticulture and Sustainability.