Which garden plants work in symbiosis and which are harmful?

Allelopathic plants -Every plant produces biologically active substances, many of which are known to herbalists and often used by humans. When we talk about this, the first thing that comes to mind are the wonderful aromas of flowers and the forest. The amount of VOCs or Volatile Organic Compounds released from plants sometimes reaches serious proportions. For example, one hectare of coniferous forest releases up to 30 kg of essential oils per day.

What is allelopathy?

The word allelopathy comes from the Greek állēlos (“one to another”) and páthos (suffering, disease or hypersensitivity).
Allelopathy teaches us how compounds released by plants affect the growth, survival or reproduction of other organisms and especially other plants. For gardening it’s simple, which plants are beneficial to each other when planted together, and which should be at a distance.
An example of classical allelopathic coexistence is the trio called by the Indians in North America “three sisters”. Corn, climbing beans and pumpkin. They are always grown together because each of them contributes something to the “trio”. The corn stalk serves as a support for the bean. The large leaves of the pumpkin cover the ground, thus protecting the soil from overheating and inhibiting the growth of weeds. Fast-growing beans, in turn, fix nitrogen in the soil, which helps the growth of corn and pumpkin.

Flycatcher effect

Many pests and pathogens usually attack only one plant or group of host plants. When fragrant herbs and flowers are planted between these plants, the pests find it difficult to identify the plants they feed on.

Plant protectors

In the plant kingdom, it’s always a fight for nutrients, water and light. But some plants often take on the role of a knight in shining armor :). The aromas or other compounds they emit repel or mislead and confuse leaf-eating insects.
Some of this knowledge was gained in a purely empirical way. People observed what was happening in the garden, or in the field and the forest. Much of it has already been confirmed by research that explains exactly how the interaction takes place.

Some of the plants that can be easily grown in a symbiosis in an urban garden:

• If you are planting roses or strawberries, remember that their best friend is garlic. When planted together, it protects them from fungal diseases due to its bactericidal and fungicidal properties. The volatile compounds also repel slugs, which otherwise love strawberries. Garlic is generally good for plants that are susceptible to fungal diseases – tomatoes and cucumbers, for example.
• If you decide to grow onions, it is good to plant carrots next to it. They help each other – the onion repels the carrot fly, and the carrots repel the onion fly. Rosemary and sage can also be very useful against the carrot fly.
• Marigold, sown between vegetables, repels aphids and leaf-eating caterpillars.

• Both calendula and tagetes successfully protect onions and garlic from nematodes (roundworms, often parasitic). Tagetes also has a hidden weapon – its roots secrete substances that attract and then poison the nematodes.
• Calendula and marigold are my personal favorites, and for the second year I have been patiently scattering them all over the garden. They emit a characteristic odor that repels many pests.
• Borage or starflower is a wonderful flower and good companion for many plants. If you plant it with your tomatoes and or kale, it will keep the caterpillars away. The borage flowers attract pollinators. So if you have planted zucchini or cucumbers, it will help to pollinate them.

• Most flowering aromatic plants also attract insects that are useful to the gardener. Not only pollinators, but also predators that feed on leaf-eating insects. The favorite ladybug of all children is a small but very effective predator. It can eat 150 aphids a day! Ladybugs love marigolds. So plant a few pots of marigold and keep them next to your pots of vegetables. This will not only provide the first line of protection for your plants, but will also attract useful allies!

Plant helpers

Perhaps the most famous partnership amongst plants is between tomatoes and basil. They are a great partner not only in the salad, but also in the garden. Experienced gardeners say that if you plant basil next to tomatoes, they will not only grow faster, but will also have a richer and better taste.

Self-sacrificing plants

Tropaeolum commonly known as nasturtium, in addition to delighting us with its beauty, also serves to attract black aphids. If there are nasturtiums planted next to your vegetables, aphids will prefer them and your plants will be saved.

Basic principle of interaction

Even if you know nothing about the potential interactions between plants, there is one basic principle you can follow. Plants from the same family have identical nutritional needs and compete if they are too many and too close to each other. They also suffer from the same diseases and pests, so avoid planting them close to each other!

Families in the garden

Potato family – potatoes, pepper, tomatoes, eggplant, tobacco, hot peppers, physalis, petunia, goji berry
Pumpkin family – pumpkin, zucchini, cucumbers, watermelon, melon, kiwano, loofah, tea
Legumes – beans, peas, lentils, chickpeas, soybeans, alfalfa, clover, peanuts, beans, fenugreek
The Styrian family – red beets, spinach, chard, quinoa, amaranth
Onion subfamily – onion, leek, garlic, shallot, yeast, samardala, shives (Siberian onion)
Family Compositae – lettuce, artichoke, sunflower, chamomile, dandelion, calendula, yarrow, white wormwood, chicory (blue bile), coltsfoot, burdock, tarragon, echinacea, immortelle, edelweiss, milk thistle, cornflower, daisy
Umbelliferae family – carrot, celery, dill, parsnip, cumin, coriander, parsley, fennel, anise, devesil
Cruciferous family – cabbage, turnips, cauliflower, broccoli, horseradish, kale, radishes, mustard, Brussels sprouts, alabash, shiboy
Family Ustotsvetni – basil, mint, lavender, thyme, oregano, sage (sage, lemon balm, savory

For even greater precision in choosing what to plant next to each other, you can use the table created by the IDEP Foundation.
When planning what vegetables to grow, plan to plant a plant friend next to them. Allelopathy tips will not only help you grow healthier plants, but will also make your garden a colorful and beautiful picture of vegetables, herbs and flowers.

The link to IDEP companion planting chart.

Next time we will talk about something favorite to most gardeners – micro plants.
And remember – He who creates a garden, cultivates happiness!