Sacrificial planting, or companion planting is a practice of planting specific types of plants around the borders of a garden/field or interspersed with the purpose of attracting pests (typically insects) away from other crops. This is a great way to help the organic gardener with their battle against pests without the use of insecticides.
The milkweed (Asclepius Tuberosa) is an example sacrificial plant as it is used to draw away orange aphids. (Seen in picture above.) The aphids are food to ladybugs and other predators, which go on to help control pests elsewhere in the garden.
Milkweeds also have a awesome side affect of being the plant of choice for the Monarch Butterfly to lay its eggs. This is extremely fun for my three boys who love to watch the caterpillars spin chrysalises and in turn become butterflies!
Side note about Monarchs is that they will only lay their eggs on milkweeds. Milkweeds contain a potent heart poison, which helps to protect them from browsing animals and leaf-eating insects such grasshoppers. Monarchs are able to store this poison within their own bodies, making themselves poisonous in turn. They are very brightly colored, both as a caterpillar and as an adult, to advertise that they are not good to eat. Whenever an insect is brightly colored, rather than camouflaged to match its background, it usually means they have a secret weapon. It may be bad to eat, such as a Monarch, or it may have a potent defense, such as bees and wasps.
Since these plants sustain quite a bit of abuse, they do tend to become ratty after a while… Once this occurs, I cut them back to about 6 inches tall and then they will grow back in short order.