Dalmatian chrysanthemums (Chrysanthemum cinerariaefolium) form an attractive garden plant, with their white, daisy-like flowers, and are the source of the organic insecticide, pyrethrum. Although they don't look much like typical chrysanthemums, cultivation is similar. Does this Spark an idea?
Climate and Soil Conditions
Dalmatian chrysanthemums produce most pyrethrum in high altitudes of tropical climates. However, they are tolerant of a range of conditions. In the United States and other temperate countries they grow best in a mild climate. They concentrate most pyrethrum in dry, lime-rich and fast draining soil. Plant the species in full sun. Although Dalmatian chrysanthemums can tolerate temperatures down to minus 10 degrees Fahrenheit, in colder regions it is advisable to mulch the plants heavily for winter.
Care
Basic care consists of continuous weeding, as this species is overwhelmed easily by fast growing native species. Watering rarely is necessary except during very dry spells. Extra phosphorus can increase the concentration of pyrethrum, but other fertilizers have little effect. Watch out for thrips on the plants and treat if they are present in abnormally large numbers. Chrysanthemums deter most pests with their own natural defenses.
Harvesting
To make use of the insecticide properties of this species, harvest your own supply. Collect flowers during a hot, dry period. Select fully opened flowers rather than buds. When picked, spread them out on a tray and let them dry in a warm room. Turn the flowers occasionally. When they are fully dry and crisp to the touch, you can turn them into a mild insecticide.
Insecticide Extraction and Use
Store the flowers until needed in a dry place. To prepare an insecticide, crush the flowers to a powder between your gloved fingers or with the aid of a mortar and pestle, which shouldn't be used for culinary purposes afterwards. Mix the powder with water to form a spray. Soak ½ to 1 oz of the crushed flowers in about 10 pints of water for three hours. Use the spray as soon as possible.
Precautions
Although organic, homemade pyrethrum insecticides still are toxic, especially to aquatic life. Do not use your dust or spray anywhere near ponds. Also, be careful when spraying that you do not kill all the beneficial insects on a plant as well as the pests. Picking off ladybugs beforehand helps, as does targeted spraying. Rather than indiscriminately spraying your entire garden, focus on the areas of particularly high aphid or other pest infestation.
Tags: Dalmatian chrysanthemums, most pyrethrum, this species, with their