Strawberry plants produce long stems from the central "mother" plant. The long stems are called runners, and along each runner, two or three small strawberry plants will begin to develop. They are usually a foot or more apart along the runner. When the "baby" strawberry plants contact soil, they root and grow. Unchecked runners will turn a strawberry patch into an unruly web. Control the runners on your strawberries to keep a neat patch, and also to keep the runners from stealing the energy the mother plant needs to produce berries.
Prepare a new planting area for the baby plants you will take from the runners. It should be in full sun with good drainage. Till the area so the soil is fine, and mix in some compost.
Select the developing strawberry plants that are on runners. You can root them two ways. One way is to snip the runner from the mother plant, and then snip out the baby plants you want to use, leaving some runner stem attached to the baby. Plant the baby on the shallow surface of the prepared bed, and weight it in place with a small stone on the runner stem. The baby plant must make contact with the soil, and in a few days it will have roots.
Select runners with developing strawberry plants. A second method of starting strawberry plants from the runners is to place the baby plants in the soil around the mother plant, or in small pots of soil near the mother plant, and weight them in place by putting a small stone on the stem near each plant. In a few days, when the babies have rooted, snip the runners and snip apart the baby plants. Transplant them to a prepared planting area.
Carefully set the rooted runner plants at the proper planting depth. The roots should be covered with the fine soil, the crown of the strawberry plant should rest just at the soil level. If the crown is below the surface level, it is too deep and the plant will rot. If the crown is above the surface level, it is too high and the roots will dry out.