Volunteer plants are plants that germinate and grow in areas where you did not plant them. In roses, young shoots may appear several feet from the base of the bush. It is doubtful (although not impossible) that these plants sprouted from seeds. It is more likely that these volunteer plants are suckers growing from the root of the rose bush. Although this may seem like a free source of new roses, the sucker may not produce true to from and may grow into an inferior rose, as most roses are grafted onto a rootstock that differs significantly from the resulting plant
Remove the sucker from the root of the rosebush with a pair of garden clippers. Make a clean cut at a 45-degree angle. Remove foliage from the lower half of the cutting. This allows the plant to concentrate its energy on root formation.
Pour powdered rooting compound into a paper cup. Dip the bottom 2 inches of the stem into the rooting compound. Tap the stem on the rim of the cup to remove any excess rooting hormone.
Plant the cutting to a depth of 3 to 4 inches in a 4-inch pot filled with a mixture of equal parts peat moss, potting soil and either vermiculite or perlite. Water to moisten the soil, but don't make it soggy.
Place a dowel or pencil in the soil midway between the cutting and the rim of the cup. You will use the dowel to support a plastic covering to maintain humidity and speed rooting. Check that it is securely in the soil.
Cover the pot with a clear plastic bag. A large food storage bag or clear plastic bag from produce purchased at the grocery store works well. Set the pot inside the bag, pull the top over the top of the rose plant and tie with a twist tie.
Place on a windowsill that receives bright indirect light. Too much sunlight may overheat the plant inside the bag.
Monitor the plant closely. If you observe any signs of mold or mildew, open the bag and allow air to circulate. Puncturing a few holes it the bag allows plants to breathe while maintaining the humidity level needed for growth.
Remove the bag once new growth appears. Move to a sunny location until rapid growth appears. Place the pot outside in a sheltered location to accustom the plant to outside conditions. Plant in the desired location when weather is cool. Keep soil moist for the first few weeks to avoid shock to the newly planted rose.