In the Garden
Ralph Purkhiser, Purdue University Master Gardener
When we speak of migration, we usually think of the migration of animals with the seasons. We are aware that some birds that spend the summer here go south in the winter, and other birds come from more northern climates to winter here in southern Indiana. We also know about the annual migration of the monarch butterflies and other insects. However, plants sometimes migrate also.
For plants to migrate, seeds must be carried to the new location. This may be accomplished by winds or by animals. For plant migration to be completed, the conditions in the new locale must be favorable for the germination of the seeds and the development of the plant. For many years, most of southern Indiana was in the USDA plant hardiness zone 5, where minimum winter temperatures were said to drop to twenty degrees below zero. However, as the climate has changed, our minimums now are closer to 10 degrees below zero. That 10-degree difference places us in zone 6 now, and a whole new group of plants will tolerate that minimum.
That can be both a blessing and a curse. Twenty years ago, one rarely saw crape myrtles growing in Indiana. Now, the combination of breeding plants to tolerate colder temperatures and the climate change has made the summer bloomers quite common. Native plants that grew farther south have begun migrating northward, increasing the possibilities for our landscapes. This also enables the animals that feed on these plants to also migrate northward.
On the other hand, it opens us up to a whole new group of invasive plants that could potentially alter entire ecosystems. Kudzu has long been called “the plant that ate the south”. Kudzu has now been found growing in southern Indiana and is moving northward. This aggressive vine can cover trees and even houses in a short time, smothering the native plants. This also means that the wildlife that needs the native plants to survive will move out of the area. Another dangerous plant that is becoming increasingly common in southern Indiana is poison hemlock. In addition to taking up the growing space of native plants, this plant is seriously a threat to anyone who touches it. The threat is so serious that organized eradication efforts need to get underway. If the plants mature, the seeds produced will be carried and this dangerous plant will continue to migrate.
Awareness is the key to living with plant migration. Everyone needs to be alert to plants that may become problems, but at the same time to welcome the chance to grow new things.