It sounds as if your passion fruit plant is relatively old. From my understanding, passionfruit vines are short-lived, most dying within 5-7 years. If you have a vine planted outside that seems happy and productive, I would suggest leaving it in the ground. The stress of transplant into a different type of media may very well kill your vine. Fortunately, there’s a solution! It is quite easy to start passionfruit vines from seed. If possible, use seed from the old vine you were hoping to take with you. As you would be starting with a young plant a smaller pot would be okay, about 5-7 gallons. For your large vine the smallest pot I’d recommend would be about ten gallons. The larger you can afford to carry onboard, the better. Based upon the size of the vine at the base, I think it would be happiest in at least a 20-25 gallon pot. Soil is ideal, however it’s possible to get away with a lighter media such as coco coir. If you do decide to go the coir route, you’ll have to amend the soil with granular fertilizers. Follow these steps for growing Passion fruit in containers using coco coir media.
1. Transplant your vine. Gently loosen your vine from it’s current pot. Softly massage the roots, removing as much soil as possible. Be careful not to break the roots. Fill a pot with coco coir media mixed with a balanced (5-5-5) granular fertilizer at the recommended rate on the label. Dig a hole large enough to bury the passionfruit roots in the coir media. Place the plant into the hole, and cover with more coco coir/fertilizer mixture. Staking or trellising may be necessary depending on the size of the vine.
2. Watering deeply and thoroughly. Make sure at least 15-20 percent of the total water put into the pot flows out the bottom. Make sure your media dries out between waterings, check this by sticking your finger into the growing media up to your second knuckle to gauge the moisture level. Passionfruit can be prone to root rot, and need to dry out in order to prevent this. Good watering practice is key to your passionfruit thriving. Coco coir is known to dry out slightly faster than peat or soil based mixes. At least once per day or every other day will likely be necessary.
3. Feed your plant on a schedule. Plants prefer relatively stable conditions, and can thrive when given proper care. Look for a fertilizer with a 10-5-20 ratio, as this will help encourage vegetative production as well as fruit production in the summer. Granular or
4. Protect your passionfruit from the elements. Wind and freezing temperatures can easily injure sensitive vines. Avoid putting your vine in a windy corridor, and make sure to protect it from frost and freezing temperatures. Trellis and stake as the plant grows, giving it ample space to produce delicious passionfruit.