If you live in U.S. Department of Agriculture plant hardiness zones 6 through 9, you can winterize your passionflower plants with only a heavy application of mulch. If you live in colder climates, however, passionflower winterization becomes a little bit more complicated. Passionflowers will not survive outdoors during harsh winters, so you need to dig them up and keep them inside until the weather warms up. Although this might sound easy enough, caring for passionflowers indoors is a high-maintenance project.
Trim back any dead, dying or diseased limbs on your passionflower plant. Do this near the beginning of autumn. Remove any stems that are broken or brown.
Transplant the passionflower to a large clay planting pot. Dig a hole as large as the pot around the plant and remove the passionflower, soil and all, and place it in the pot. If you need to fill in more space, use soil from the area directly around the plant. This will help to avoid shocking the plant with different pH and nutrition levels.
Maintain a constant pH level between 6.5 and 7.5. Buy soil-testing kits from your local garden center, as well as lime and sulfur. If the pH level is too high, treat with sulfur. If it’s too low, treat with lime. Follow the instructions on the packaging for the specific amounts to use for the amount of soil in the pot. Test the pH levels at least twice before transplanting the flower back outdoors.
Set the pot in a bright spot, but not directly in the sunlight. Water sparingly with a spray bottle. Feel the soil’s surface before watering — if it feels dry, spritz it until it is just moist.
Set the pot outdoors on days when temperatures exceed 50 degrees Fahrenheit. Place the pot in partial sunlight and bring it back indoors when temperatures start to drop below 50 degrees. When all danger of frost has passed and temperatures remain constantly above 50 degrees, you can replant the passionflower in its original location.