I've been growing seed-raised Black Passionfruit plants for sale for over a decade and the vast majority of my customers lament that they've grown a grafted plant only for the graft to die and the rootstock take over. The most likely rootstock culprits are Banana Passionfruit and an ornamental Passiflora - both can quickly become resilient weeds. The best way to avoid this is to grow seed-raised Passionfruit. For many years they were hard to buy but they're becoming more available in Nurseries these days. I only grow seed raised plants.
Passionfruit are a tropical fruit and can be fickle in the southern states of Australia however you'll have success if you give them what they need:
Position - They like a sunny spot all year round but if you give them more than 8 hours of direct sunlight during their growing and fruiting times (Spring-Summer) you'll be rewarded. They prefer an Easterly or Northerly aspect, well drained soil and don't compete well with tree roots. Frost protection is a must. Try not to disturb the roots by digging around the base.
Protection from damaging winds - With adequate support Passionfruit will hang on through windy days however constant strong wind exposure will weaken the plants, damage leaves and blow off precious flowers. No flowers, no fruit.
Support for climbing - Passionfruit have tendrils which, once they latch onto something, hold on tight. The more opportunities you can give the plant to support itself, the stronger it will be. A benefit of growing it on support that you've created is that you'll have some control over where that baby will grow.
Fertiliser - I recommend putting a piece of offal below your Passionfruit at the time of planting. It'll give the plant a great iron boost. An ox heart or sheep liver is usually used. Make sure there is about 3 inches of soil between the root ball and the offal. You can also use pelletised chook manure.
The biggest issue with Passionfruit is that they're not fed enough and/or at the wrong time. When fertilising give your plant a healthy dose of blood and bone, dynamic lifter or aged chook manure up to a metre around its base. Feed the plant heavily in Spring before flowers and Autumn after fruit. Avoid feeding the plant whilst flowering or fruiting as Passionfruit have been known to drop flowers and fruit in favour of leaf growth if fed during these times. You can give the plant diluted liquid fertiliser any time.
Mulch - Passionfruit will appreciate a heavy mulch a metre around its base. Part of their root system is shallow and welcomes the added moisture retention from mulch and protection from the drying summer sun. Straw or sugarcane mulch is good stuff.
Water - Give 'em heaps.
Pruning - Once the plant is established, tip out the top to encourage lateral growth and promote additional side shoots which will give you more fruit. Prune your plant to a manageable height each year in early Spring. Taking about 30cm is recommended but if it's a strong plant you can go a bit harder. There's no point in letting it go beserk and the bulk of your fruit being unreachable. If the vine is too dense, thin it out a bit to promote airflow.
Extra bits - It usually takes about 18 months after planting to get a decent crop of fruit. You may get a few in the first year if you're lucky.
Keep an eye on the ground - mature fruit will drop.
YOU ONLY NEED ONE PLANT!!!
Image: By THOR (Passion Fruit Breakfast) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons