Growing Raspberries in Tunnels and Greenhouses: maximizing yield

By Adam Dale, Department of Plant Agriculture, University of Guelph

To understand how to grow raspberries under tunnels or in greenhouses successfully, the grower needs to understand the biology of the plant, and know something about the systems used in field production of raspberries. In part 1 of this series, I explained the structure of a raspberry plant and discussed various aspects of flower initiation and dormancy as they relate to protected cultivation. Here, in the second part, I will discuss such concepts as cane quality, cane density, within-plant competition, and trellising as they relate to 'long cane' production.

Cane Density

When the effect of cane number on yield is considered, the general trend is that yield per length of row increases until there are about 12-17 fruiting canes per metre. It then plateaus, and as the cane number increases starts to decrease. The optimum cane number of 12-17 per metre is for rows 2.4-2.7 m. apart. This translates into about 5-6 canes per m2 of land area. Since most canes are fruited at about 1.5 m. tall, this would give a fruiting cane length of 7.5-9 m per m2 of land area. This gives the grower a target cane length around which to design his system.

Berry size tends to become smaller the larger the number of fruiting canes in the row. Young first-year canes also affect yield through their competitive effect. The general trend is that the larger the numbers of young canes, the lower the yield will be.

To optimize the cane density in a fruiting plantation, two aspects need to be considered: row spacing and cane density within the row. Research has shown that if the rows are planted closer together the yield will be higher on an area basis. In Ontario, depending on the type of trellising and the farm machinery used, raspberries can be planted as close as 1.8 m., although 2.4-2.7 m is usual. Inside tunnels and greenhouses, closer spacing between the rows can be used.

Within-plant Competition

Within-plant competition can be altered by controlling the number of young canes that grow. There are three ways to control young cane growth and influence yields: an annual system, annual with cane vigour control, and biennial. In the annual system the young canes grow each year to fruit the following year. In the annual system with cane vigour control, the first flush of young canes is removed each year and a second flush is allowed to grow. In the biennial system, the fruiting phase is separated from cane growth. In the first year of the two year cycle only new canes are allowed to grow, in the second only fruiting canes are allowed to grow.

When the three systems are compared, there is a relationship between the vigour of the young canes and the yield of the fruiting canes; the more vigorous the first year cane, the lower the yield of the fruiting cane. The annual system gives rise to tall first year canes and the fruiting canes only give moderate yield. In the annual system with cane vigour control, first year canes are moderately tall and the fruiting canes can give between l20-l50% of the yields of the annual system. The biennial system has no first year canes in the fruiting year and the fruiting canes can give between l50-250% of the yields of the annual system.

In the annual system with cane vigour control and the biennial system, first year canes are removed when they are between l0-20 cm high. For cane vigour control only the first flush of cane is killed, while in the biennial system the canes may have to be removed three or four times until the harvest season.

Trellising

With the raspberries in narrow rows and the new cane growth carefully controlled, the canes will need to be trellised to support the heavy crop. Trellising also increases picker satisfaction and efficiency, increases yields as more of the berries will be picked, and allows a lower disease pressure as the canopy will be more open. However, effort is needed to build the system which gives the grower a larger up-front cost. There are three ways to trellis raspberries; the conventional upright system, a "V" or "T-Bar" system, where the fruiting canes are supported at an angle, and the new Stiles system, which bends the cane into the row and moves them into the correct position at flowering.

The conventional system holds the raspberry canes in a single upright row and makes picking considerably easier than if nothing is done. It allows narrow row spacing to be used but the young cane grows outside the fruiting canes. This type of system is the only one that can be used for machine harvesting of the crop at the moment. One possible method is to place 1.5m high posts, about 10m apart and hold the fruiting canes in a single line with two wires held together at about 50 cm from the ground. The fruiting canes are then tied singly or in bundles of 2 or 3 to a single wire about 1.3m from the ground.

In the "V" system, the canes are separated to form two rows which are between 0.6-0.9m apart at their tips. This allows pickers to reach the fruit very easily, particularly as the young cane grows up between the fruiting canes. The yields from this system are higher per row than the conventional system, but the rows need to be spaced further apart. One possible method is to place posts at the same distance apart as in the conventional method and a horizontal bar 0.6-0.9m long is attached to the post to make a "T" bar configuration. Single wires are then placed on the end of each arm and the canes tied to these wires.

In the Stiles system, designed by Dr. Herb Stiles, VPI & SU, Virginia, the fruiting canes are supported on a swing trellis. This trellis is placed so that initially the fruiting cane is bent at about 45 cm by an off-set wire on one side of the row with the tip of the cane held equally off-set on the other side of the row. The fruiting laterals then grow towards the light onto one side of the cane. At flowering, when the lateral position has been set, the trellis is moved so that the fruiting cane becomes upright. This then presents all the fruit to one side of the row. In this system, the young cane will grow away from the fruiting canes towards the light. This system has many advantages as all the fruit is presented on one side unobstructed by the new canes.

Conclusions

We can learn how best to maximise yield in tunnels and greenhouses from research and growers experiences with field production of raspberries. So in tunnels and greenhouses, I have the following recommendations: keep the canes in the rows in a band no wider than 30cm, with at the most 1.8m between the rows; leave 7.5-9m of fruiting cane per m2 of land area; control the vigour of the primocanes by removing the first flush when they are 10cm tall; trellis the canes and consider the Stiles trellis.
However, for someone to grow a good crop of raspberries they need to understand the basic biology of the raspberry plant as this enables them to make good decisions regarding the plant husbandry. Also, careful attention to management factors such as trellising is required so that the plantings in tunnels and greenhouses are easily accessible for pickers to harvest the crop. In this and the first article, I have explained some of the basic biology of the raspberry and some of the standard cane management procedures. These, together with good plant and harvest management can make the raspberry a highly profitable crop in tunnels and greenhouses.

Tunnel picture

Figure 1: Tunnel picture


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