Again, plant species added for this purpose must be selected carefully because they may also cause an increase in the population of pests. Plantings can be diversified in several ways. Depending on the situation, one or more of the following systems can be used. A mixture of plant species, from annual herbaceous plants to perennial shrubs and trees, can be planted on the edges of crop fields, along fencerows, or in woodland clearings. These strategies are especially useful for annual crops, and also help keep troublesome weeds under control.
Some insectary plants are also valuable as cover crops and can be used to enrich the soil as well.
Hedgerows Hedgerows can increase the number of beneficial insects by providing shelter and alternative sources of food. Wild plants and hedgerows growing on uncultivated land also provide alternate sources of food for beneficial insects when prey populations are low. Hedgerow plants leaf out in the spring, well before most crop plants. They support insect populations which provide food for the beneficial insects and allow the beneficials to produce an early generation. This early generation of natural enemies will then move into the crop fields as pest populations begin to build.