I live in Charlotte NC. I understand the vine of the passion flower dies back in winter, but should I cut down to the root before or after a hard freeze and mulch it, or not cut down at all? It is over 15 feet long.
While these plants will normally die down for winter dormancy, thus, not requiring too much pruning, since yours is quite large, cutting it back by about a third (or even half if not more) might make it easier to fit the plant inside. Here is an article or two on overwintering passion flowers that you may find helpful: https://www.gardeningknowhow.com/ornamental/vines/passion-flower/preparing-a-passion-flower-vine-for-winter.htm
https://www.gardeningknowhow.com/ornamental/vines/passion-flower/passion-flower-winter-care.htm
Companion planting for passion fruit and how to prune.
This article will help with pruning:
https://www.gardeningknowhow.com/ornamental/vines/passion-flower/cutting-back-passion-vines.htm
As far as companion plants, are you looking for something that will grow at the base, or a vine that will grow among the passion vine? Let me know and I can better advise.
I am trying to eradicate a passion flower which is taking over the garden. Could you help with advice about week killer, etc.?
Some species of passionflower can be invasive and extremely hard to kill.
Here is an article that will help you control and get rid of passionflower vines:
https://www.gardeningknowhow.com/ornamental/vines/passion-flower/maypop-weed-control.htm
My passion flower had numerous beautiful blooms and the vines were healthy. It grew extensive with the vine structure being much thicker than the previous year; however, only two blooms appeared all summer and they were much much smaller than those of the previous year.
Also, only two fruit appeared whereas the previous year many fruit appeared. I fertilized the plant once during the spring. What can I do to make my plant more productive as far as blooms and fruit?
It sounds like you may have given the plant too much nitrogen. This causes vigorous growth but little in the way of blooms. You can counter this with adding more phosphorous to the plant. Bone meal is an excellent source of phosphorous.
I have just taken delivery of two passion flower plants: one is Passiflora Andy and one is Passiflora caerulea "Clear Sky." They both have flower buds. Can I plant these outside or is it safer to keep them indoors until the spring?
Unless you live in a very warm climate, it is best to keep them indoors until spring.
What causes passion flower plants to lose buds and not bloom? We're in sunny Florida in Bradenton area....lousy soil for the most part.
Is your passion flower getting direct sunlight all day? Is it getting enough water? Have you been fertilizing?
There are four possible reasons your passion flowers are dropping buds and they have to do with pollination, environmental reasons, the soil fertility and thrips. Since you said you had "lousy soil" let's focus on that first. I would recommend applying fertilizers at least four to six weeks prior to the onset of flowering.
I would also like you to examine your passion flower for thrips. Is there any blotching or streaking on the petals? If you do find thrips, there are environmentally safe insecticides, such as Spinosad, that you can use.
For more information on the other causes of bud drop, please visit the following link:
https://www.gardeningknowhow.com/plant-problems/environmental/why-healthy-blooms-fall.htm
For more information on thrips, please visit the following link:
https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm
For more information on growing passion flowers, please visit the following link:
https://www.gardeningknowhow.com/ornamental/vines/passion-flower/passion-flower-care.htm
If a plant is root bound, do I cut some roots when transplanting? The plant is a very large purple passion in a 6 in. pot and has branches from 2 ft. to 10 ft. long. It is so beautiful but seriously root bound. And can I cut some of the branches off and use for starters at same time?
If a plant is rootbound you have these options: re-pot in a bigger container, prune the roots and re-pot in the same container or divide the plant, if appropriate.
And, yes, you may take stem cuttings and root them to propagate your plant.
These articles will explain those options in more detail:
https://www.gardeningknowhow.com/plant-problems/environmental/root-bound-symptoms.htm
https://www.gardeningknowhow.com/houseplants/hpgen/learn-more-about-repotting-houseplants.htm
https://www.gardeningknowhow.com/houseplants/hpgen/prune-roots.htm
https://www.gardeningknowhow.com/ornamental/vines/passion-flower/propagating-passion-flower.htm