To optimize yields and reduce the use of chemical products, intercropping is a natural and effective method. Among the most versatile vegetables, three combinations stand out for their synergistic effects: tomatoes, carrots et onions. Their strategic combination repels parasites, stimulates growth and improves disease resistance.
Celery, a natural ally against parasites
Celery, often overlooked, plays a vital role in protecting cabbages. Its smell repels Pierida butterfly whose caterpillars devour cabbage leaves. In return the cabbages protect the celery rust thanks to their deep root system. This reciprocity makes them an ideal trio for cabbage and celery crops.
Because this association works
- Insect repellency : The aromatic compounds in celery act as a natural repellent.
- Stimulation of defenses : Cabbage roots release substances that inhibit pathogenic fungi.
The tomato, the cornerstone of associated crops
The tomato is a central vegetable in many associations. It benefits from the presence of marigoldswho reject the nematodes and stimulate fruit production. In return, tomatoes protect strawberries from putrefaction thanks to their smell.
The best companion plants
- Basil : Repels nematodes and improves the flavor of tomatoes.
- Nasturtiums : Attracts aphids, limiting their impact on nearby crops.
- Parsley : Stimulates growth and strengthens resistance to diseases.
Onion, natural guardian against parasites
Onion, garlic and leeks form a formidable alliance against carrot flies and onion. Their powerful scent repels these insects, while carrots mutually protect onions from their pests.
Effective planting methods
- Alternation of lines : Alternate onions and carrots in parallel rows.
- Chives on the edge : Plant chives around carrot squares to reinforce protection.
The scientific mechanisms underlying these associations
The interactions between vegetables are based on complex biological principles. Understanding these mechanisms allows you to optimize associations and avoid common errors.
Chemical repulsion by volatile compounds
Plants emit volatile organic compounds (VOCs) which act as repellents or attractants. For example, onions release sulfides responsible for their characteristic odor, repelling carrot flies. This property explains why onions and carrots are often planted together.
Concrete examples
- Garlic and strawberries : Garlic prevents strawberries from rotting thanks to its antifungal properties.
- Celery and cabbage : Celery emits terpenes that interrupt pierid behavior.
Radical competition and symbiosis
Some plants modify the soil in ways that benefit their neighbors. Cabbages, with their deep roots, drain nutrients into the surface layers, benefiting celery. On the contrary, legumes (beans, peas) fix nitrogen, but their association with onions is not recommended due to their incompatibility.
Mistakes to avoid in company
While helpful, the company requires careful planning. Some associations, while popular, can harm cultures.
Combinations to avoid
- Beans and onions : Legumes and alliaceae (onion, garlic) damage each other.
- Tomatoes and cucumbers : Both plants attract the same pests, increasing the risk of contamination.
- Cabbages and leeks : Their proximity favors the spread of fleas.
Practical case: avoid legumes near alliaceae
A gardener planted beans next to onions, causing both crops to slow down. The solution: separate these vegetables with a row of carrots or salad greens.
Crop rotation, a crucial step
Companion planting does not replace crop rotation. Planting the same vegetables in the same place year after year depletes the soil and encourages disease.
Ideal rotation scheme
- Year 1 : Tomatoes + marigolds + basil
- Year 2 : Carrots + onions + chives
- Year 3 : Beans + corn + pumpkin
Planting techniques to maximize effects
The effectiveness of the associations depends on the spatial and temporal arrangement of the plants. Here are proven methods to optimize yields.
The companion square method
This technique consists of creating 1 m² squares by grouping complementary plants.
Example of a tomato square
- Center : 3 tomatoes
- Edge : Marigolds and basil
- Coining : Parsley and chives
Advantages :
- Circular protection : Peripheral plants repel pests.
- Cross-stimulation : VOCs from marigolds and basil increase production.
Alternate rows for carrots and onions
For row crops, alternating onions and carrots provides mutual protection.
Plant diagram
- Row 1 : Onions spaced 15 cm apart
- Row 2 : Carrots sown 2 weeks later
- Line 3 : Chives or leeks
Result : Onions repel carrot flies, while carrots mitigate attacks on onions.
Alternatives to the three top vegetables
If these combinations aren’t right for your yard, other combinations offer similar benefits.
Cabbage and horseradish: an alliance against rust
Horseradish, with its powerful roots, secretes antifungal compounds that protect celery from rust. This combination is especially useful in humid regions.
Salads and radishes: a defense against fleas
Salads planted near radishes or turnips prevent their leaves from being punctured by flea beetles. Salads absorb attacks, preserving the most valuable crops.
Pumpkin and beans: a nutritious symbiosis
Beans fix nitrogen, benefiting squash. In return, the squash shades the soil, limiting the growth of weeds. This combination is ideal for organic gardens.
: towards a resilient and productive vegetable garden
Combining tomatoes, carrots and onions offers a sustainable solution to increase yields. By combining these vegetables with suitable companion plants, gardeners reduce their reliance on pesticides and improve the overall health of their garden. Experimenting with these associations, respecting the rotations, allows you to create a balanced ecosystem where each plant plays a specific role.
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