The plant is famously used in companion planting with many vegetable crops to repel harmful insects. The growing plant repels whiteflyand can be grown near tomatoes to keep the crop free of the insect.Secretions from the roots of the plants have an insecticidal effect on the soil, with a broad spectrum of activity. it is effective against many species of nematodes. For this reason it is used commercially as a form of green manure.

The secretions are produced about 3 to 4 months after sowing. It is very effective when used prior to planting strawberries and roses and with tuberous crops such as potatoes.

Sowing: Sow in spring from early February to the end of May
Sow in a propagator at room-temperature from mid February to mid April. Sow under cold glass in a cold greenhouse or coldframe from mid March to the end of April. Or sow seeds directly outdoors 2 weeks before the last frost in April to the end of May. Stick the seed vertically into the compost.
Germination usually takes 5 to 14 days. Tagetes seeds germinate quite fast when exposed to humidity, after which the plant develops more slowly.

Sowing Indoors:
Use pots or trays of moist seed compost and cover with a very fine sprinkling of compost. The optimum growing temperature is around 21°C (70°F). After sowing, keep the surface of the compost moist but not waterlogged. When large enough to handle, transplant seedlings into 7.5cm (3in) pots to grow on. Harden off and plant out in full sun, after all risk of frosts (normally mid to end of May).

Sowing Direct:

Sow thinly, 6mm (1/4in) deep in drills 30cm (12in) apart in well-cultivated soil which has been raked to a fine tilth. Water ground regularly, especially in dry periods. When large enough to handle, thin out until they are finally 15 to 22cm (6 to 9in) apart.

Cultivation:

Keeping the plants well dead-headed makes them practically perennial!Plants in full soil will benefit from a foliar feed every 2 weeks. Plants in baskets and containers require a fertiliser each week. Use a feed with balanced N and P (e.g. NPK 15-15-15). Don't apply fertilisers which contain ammonium when temperature has dropped below 17°C.