Pyrethrum - Chrysanthemum cinerariifolium (Tanacetum cinerarifolium)
Quarter of a teaspoon of open pollinated seeds from our gardens for $4.00.
Pyrethrum is a perennial herb that grows to about 30cm. Pyrethrum prefers an open sunny position with well drained soil. It likes good air movement around it and doesn’t like to be overgrown by other plants. Plants can be divided in autumn to produce more plants.
Sow seeds in spring, sprinkle seeds and cover with a fine layer of potting mix. Water and keep damp not week. Seeds take approximately 14 days to germinate. Once seedlings have developed a couple seeds of true leaves they are ready to be transplanted into the garden or into larger pots.
Using Pyrethrum in the Garden
Pyrethrum is effective against a wide variety of insects, including soft-bodied insects and chewing and sucking insects such as aphids, leafhoppers, mealybugs, spider mites, stink bugs, scale, thrips, and whiteflies. The insecticidal activity of this potent organic compound targets an insect’s nervous system, paralyzing (on contact), thus leading to its death.
I have my plants growing at the base of my apple trees to help with the management of coddling moth. Since I like to keep things simple, I just leave mine to flower and drop to the ground when they have finished.
But you can collect the flowers when they have dried on the plant, ground the seeds and sprinkle over infested plants or around the base of problem plants/areas.
Pyrethrum Spray will kill any insect that comes into contact with it, including beneficials like ladybugs, lacewings and bees. Because it breaks down rapidly when exposed to air and light, it can be applied in a way that shields beneficial insects from danger, but gardeners absolutely must use this chemical properly and only apply during late evening, night or very early in the morning, before bees are out foraging. Use it as a last resort.
Coarsely grind the dried flower heads and to every firmly packed half-cup of flowers, add 1 litre of warm water. Cover and leave to stand for three hours, strain and add a teaspoon of pure soap and one of cooking oil. Shake well before use. Don't spray in temperatures over 32°C. The spray will kill bees so use it when they are not active — in the early morning or evening. This spray will only remain potent for about 12-24 hours so any that is not used should be discarded after this time. Remember that even though this is an organic spray it will also kill beneficial insects so only use as a last resort.
A more effective spray can be made by covering flowers in alcohol such as brandy or vodka and leaving for a couple of days in a dark place. Use by straining off liquid and adding 6 parts water to 1 part concentrate. Use immediately.
Pyrethrin insecticides are biodegradable and will break down within a few days in direct sunlight. The insecticide does not persist in the soil or on the crop, which is why it is relatively safe to use within a vegetable garden.
When using pyrethrum, take the same precautions you would with any chemical.
Although relatively harmless to people, pyrethrum is still a poison so baits, dust and sprays need to be carefully labeled and stored out of the reach of children and pets. The flowers and dust will maintain their potency longer if stored in the fridge.
Reference: Organic Gardener, Gardening Know How and The Spruce