Proper training and pruning of the vines will enhance the benefits of good support structures and planned orchard layout. Further advantages are gained by well maintained grass strips between rows to facilitate access and provide ground cover.

Added nutrients will usually be required to produce the best growth, as soils in areas where passionfruit are grown are generally of low fertility. Irrigation will be needed if soil moisture is likely to be inadequate during summer.

TRAINING

When training the vines the aim is to get them on to the wires of the trellis as quickly and simply as possible.

Push light stakes into the ground beside each plant and attach them to the wires in a fan to provide support for the young leaders. Two or four stakes may be used, but even a single vertical stake will suffice.

When the young vine starts to grow, choose the four strongest shoots and direct them up the stakes. Remove all other shoots to encourage maximum growth in the leaders.

Passionvine trellis elevation: (A) main leaders; (B) secondary leaders; (C) post; (D) bamboo or manuka stakes; (E) 2.5mm high-tensile wire; (F) vine plant; (G) laterals

As each leader lengthens, twist it lightly round the stake and tie it in position. Once the leaders reach the trellis wires, train two along the lower wire, one to the left and the other to the right, and the two similarly along the top wire.

At left the leaders are well trained along and onto the supporting wire, making them suitable for mechanical pruning. At right the leaders have not been trained properly, and a mechanical pruning would be likely to cut the leader and thus cause a significant reduction in the fruiting canopy

Double-planted vines are often trained in one direction only.

Two or three branches from each main leader can also be trained along the wires to serve as secondary leaders. The leaders should be twisted loosely around the wire and again tied in place.

All other shoots thrown out by the plant at ground level should be removed before they exceed 8 cm.

It is important that a lot of care and attention is put into the training of the leaders along the wire, avoiding loops that hang down well below the wire, so that pruning in future seasons can be streamlined and mechanised.

In the spring following planting the vines make considerable growth, and further careful training and tying is necessary to keep the leaders on the wire until they meet up with the neighbouring plant. Laterals arising from these leaders will flower and fruit that season.

PRUNING

The passionfruit vine bears its fruit on the current season’s growth, so careful pruning is essential.

If the vine is left unpruned, the bearing surface becomes further and further removed from the leaders. As there is no room for unlimited expansion along the trellis the annual extensions become intertwined among themselves, and with the growth of previous seasons and of neighbouring vines. The result is a mass of tangled growth, and the vine will be short-lived because disease become rampant as the density of growth prevents adequate spray coverage.

Pruning passionfruit. Leaders well trained into the wires facilitate mechanical pruning.

No pruning is necessary until the second spring after planting. Annual pruning is necessary from then on, and should be done in late September or early October, when the plants are beginning to grow vigorously. Earlier pruning may result in the vines dying back.

On young vines in particular there is often the remainder of an off-season spring crop at normal pruning time, and there is a temptation to delay pruning until all this fruit has been harvested. This is not advisable, as by that time (November) the new growth will be well advanced and covered with flowers and young fruit, much of which will have to be pruned off. Any gain in yields from a normally light spring crop would be at the expense of the main summer-autumn crop, and overall production and returns under present market conditions in New Zealand would be reduced.

In localities free of frost there is merit in late pruning (November to early December) to produce a winter crop, the yield of which is usually much reduced. However, as this is a period of low supply and high returns on the market, the extra effort can in some instances pay off handsomely.

When pruning, shorten all laterals to 10-15 cm below each wire, then remove all dead, diseased, and weak growth. This can be done mechanically with a motorised hedge trimmer, or even by hand, using hedging shears. To prune each vine individually with secateurs is time consuming and not economical when compared to more streamlined methods.

If a vine needs a replacement leader, pruning may have to be done by hand, or provision made for a suitable replacement leader, before the wholesale removal of excess growth.

This sketch illustrates passionfruit vine before pruning (at left), and after pruning (at right). Laterals should be cut back to 10-15 cm from the leader

When shortening leaders the cut should be made to a young side shoot, as dormant buds on older leaders may not shoot and dieback can occur.

Clear all prunings from the plantation and burn as a hygiene measure.

Immediately after pruning spray with a copper fungicide to check diseases. A suitable insecticide could also be applied at this time if necessary.

NUTRITION

Most soils that passionfruit are grown on in New Zealand are not naturally highly fertile.

For quick establishment of the plants it is necessary that growth is not checked or stunted by lack of nutrients. In addition to the organic fertiliser added at planting’s, a nitrogenous fertiliser should be applied over a 1-2 sq. m area around each plant every 4-6 weeks, throughout the first growing season. About 15 g nitrogen should be applied per sq. m at each application, e.g. 30 g of urea.

Once cropping begins, routine soil and leaf analysis can provide a guide to fertiliser requirements.

Leaf analysis is comparatively new in New Zealand, and more work is required to fully ascertain desirable levels. At this stage it is suggested that for a sample taken during February or March, consisting of about 24 leaves and petioles (taking the first fully expanded leaf on actively growing shoots), the range in table 1 is about right.

Most passionfruit blocks in New Zealand have high copper levels, owing to high requirements for copper sprays in disease-control programmes, and therefore have levels well above those in table 1.

Passionfruit have always been classified as having a high nitrogen requirement, and the desirable levels in the leaves are certainly higher than for most crops. Over application of nitrogen during the cropping season should be avoided, however, as it can throw the vines into a vegetative state at the expense of cropping.

Where soil and leaf analysis levels are satisfactory, but not excessive, the fertiliser programme in table 2 is suggested.

The fertiliser should be broadcast over the whole crop area.

GROUND COVER

Most passionfruit orchards in New Zealand have a grass sward between the rows, with a weed-free herbicide-treated strip beneath the vines.

The grass sward should be mown when it reaches a height of about 17 or 18 cm, down to about 5 cm. Cutting lower than this can cause baking of the soil and loss of clover in the sward during hot dry periods.

Herbicides such as Preeglone and glyphosate(Roundup) should be used with care as they will damage plants, especially glyphosphate which is systemic. Residual herbicides should not be used beneath passionfruit unless local experience has shown them to be safe.

A common practice is to use glyphosate after pruning, when the risk of contamination of the plant is least, followed by Preeglone if required. Both these materials should be kept away from the trunk, which in passionfruit stays green for several years. Damage from Preeglone on the trunk can open the way for crown canker infection.

Passionfruit orchards are not usually cultivated, but if cultivation is necessary, e.g. to control weeds, it should only be shallow to avoid damage to the root system, but bulk of which lies close to the soil surface. This is particularly important in dry areas.

Some growers allow weed and grass growth around the trunks in winter and spring to provide protection against frost. However, it is probably better to protect properly against frost with bracken fern.

IRRIGATION

In areas where passionfruit are grown at present, vines are not usually irrigated. Inadequate soil moisture, however, can cause defoliation, loss of fruit, and low yield. Irrigation is therefore beneficial during dry summer weather, especially in areas with light, shallow soils.

Young vines establish more quickly in dry years if irrigated. In normal years and on heavier soil types, care must be taken not to induce root rots with an excessive use of water.

At each irrigation the soil should be well wetted to the depth of the root zone. Frequency of irrigation will depend on the moisture-holding capacity of the soil and the weather.

Water requirement for a mature passionfruit orchard has not been worked out for New Zealand conditions but is likely to be in the range of 1.0 Et., that is, equal to the local potential evapotranspiration figure.

FLOWERING AND POLLINATION

Once new growth starts the aim is to keep the plant growing, and continually producing new flowers. Even under fertile orchard conditions this does not always happen, and it is likely to be weather related. Flowering and pollination are adversely affected by changeable weather, and probably the most important factors in New Zealand are the sudden drops in temperature that can occur, and the high chance of rain in the flowering period. Wetness causes the pollen grains to burst and become useless. Cool damp weather during flowering is not conducive to further flower production or fruit set.

Purple passionfruit are self-compatible and largely insect pollinated, mainly by bees.

The flowers are attractive to bees, having a good nectar supply with a high sugar content and a heavy sticky pollen suitable for bees to gather.

Bees are not normally introduced into passionfruit blocks in New Zealand but, if pollination is poor or fruit is lacking in seed numbers and pulp, hives could be introduced.

Temperature at pollination is probably a significant factor in successful fruitset, as with other fruits.