Mixed planting, or companion planting, is one of the oldest gardening principles. It is based on the observation that some plants benefit each other — they deter pests, improve the soil or complement each other in their nutrient uptake. Conversely, other combinations lead to poorer growth and higher susceptibility to disease.
Why companion planting matters
In nature, plants don't grow in single-species rows. Diversity in a bed brings several advantages. Some plants deter pests from others through their scent — the classic example being garlic planted among strawberries to reduce grey mould. Others attract beneficial insects: flowering herbs bring in pollinators and predatory insects. Legumes enrich the soil with nitrogen, from which neighbouring plants benefit.
Companion planting also makes better use of space. By combining deep- and shallow-rooting plants, or tall and low-growing species, you can grow more from the same area.
Proven combinations
Tomatoes and basil
A classic pairing — not only in the kitchen but in the garden too. Basil deters aphids and whitefly that attack tomatoes. Some studies suggest that basil growing near tomatoes improves their flavour. Plant basil right at the foot of the tomato plants — it will appreciate the light shade they provide.
Carrots and onions
Another well-tested combination. Onions repel carrot fly with their scent, and carrots repel onion fly. Sow alternating rows of carrots and onions. This combination works reliably and is the basis of many mixed planting schemes.
Garlic and strawberries
Garlic planted among strawberries reduces the incidence of grey mould (botrytis), which is the strawberry's greatest enemy. Plant garlic cloves in autumn between rows of strawberries, 15–20 cm apart. Both crops benefit in spring.
Lettuce and radishes
Radishes mark the rows of slow-germinating lettuce and are harvested before the lettuce needs the space. Sow them together — radishes will be done within 30 days and the lettuce can then fill the freed-up space.
Peas/beans and sweetcorn
The famous Native American "Three Sisters" method: sweetcorn acts as support for climbing beans; beans enrich the soil with nitrogen; and squash, with its large leaves, suppresses weeds and protects the soil from drying out. In Central European conditions, the combination of climbing French beans with sweetcorn works particularly well.
Kohlrabi and lettuce
Kohlrabi grows more slowly and occupies space above ground. Lettuce fills the gaps at ground level and is harvested before the kohlrabi needs more room. This combination makes efficient use of bed space.
Combinations to avoid
Tomatoes and cucumbers
Although they are often grown in the same greenhouse, tomatoes and cucumbers have different requirements. Tomatoes prefer drier air and good airflow; cucumbers want humidity and warmth. In an open bed they don't directly harm each other, but in a greenhouse it's better to keep them apart.
Tomatoes and potatoes
Both belong to the nightshade family and share diseases, particularly potato blight. Never plant them close together — infection transfers easily from one crop to the other.
Beans and onions/garlic
Alliums inhibit the growth of legumes. Both French beans and peas grow better when not in the immediate vicinity of onions or garlic.
Fennel
Fennel is notorious for inhibiting the growth of most neighbouring plants. Grow it separately from other vegetables, ideally at the end of a bed or in its own container.
How to plan a mixed bed
When planning your bed, combine plants with different heights, root depths and harvest times. Place taller plants (tomatoes, beans) on the north side so they don't shade lower-growing crops. Between slower plants (cabbage, kohlrabi) sow quick catch crops (radishes, lettuce).
Observe spacings — companion planting doesn't mean an overcrowded bed. Plants still need enough space for airflow, otherwise the risk of fungal diseases increases.
Keep records of what grows where. In the following year, observe crop rotation — it's not enough just to change the plants; whole combinations should rotate around the beds.