Answer: You may be over-fertilizing. Since Passionflower is not winter hardy in your gardening region, I hope you plan to winter your plant indoors. You can take it back outside in the spring. Outdoors, passionflower likes loose sandy or gravelly soils and does best when planted against a brick wall that retains heat during cold winter weather. Too much manure or compost will result in lush vegetative growth and poor flowering. This species will flower in a small pot, but it prefers plenty of root space and will do better in a roomy container. In Zone 8-9, the ideal location is against a warm south-facing old brick wall where an overhang prevents excessive drenching by heavy rains. Go light on fertilizer and water deeply, but infrequently; passionflowers should be encouraged to reach deep into the earth for water. When motivated to do so, they are capable of developing amazing root systems to sustain them though droughts and freezes. Passionflowers love high humidity, but they are subject to fungal diseases if they don?t get good air circulation in the greenhouse. Passionflower does better overwintered in a cool greenhouse where it can go semi-dormant as opposed to in a hothouse where it will be tempted to put too much energy into weak off-season growth. In either case, it is important to keep the soil on the dry side in the winter. Passionflower may be wound around a hoop support to keep it within bounds so that it may be grown as a houseplant in a sunny south-facing window.
Passionflowers flower on new growth, so they may be pruned early in the growing season. It is best to cut some stems back nearly to the base, rather than just trim the tips. The terminal buds may be pinched out to encourage branching. Always keep some green foliage on the plant to keep the sap rising and encourage rapid regrowth. The roots may be weakened and become subject to fungal infection if too much top growth is removed at once. Don?t try to train passionflower to be too neat and compact; branches allowed to hang loose and droop a bit will be the ones most inclined to flower. Blue passionflowers will regrow from deep roots after even severe freezes. They have been known to survive temperatures as low as 5? F when the ground was frozen over two feet deep. It is nevertheless important to keep the soil as warm as possible, especially in the winter greenhouse.
Best wishes with your passionflower.
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