Viburnum (Viburnum opulus sterile)How well established is this crop?
This crop is relatively new. It has been grown commercially for around 5 years. Commercial returns, current growers and some level of regional based research may be available to help those new to this industry.Background
Viburnum opulus ‘sterile’ is also known as the Snowball Tree and has been grown in the gardens of Otago for many years. It produces long stems with vivid green leaves and white flowers. To grow it as a cut flower the plant must be pruned immediately after flowering. This promotes long stem growth before the plant over-winters and flowers again the following spring. The plants are very hardy and will grow in almost any condition. Protection from the wind and adequate watering during the season are key requirements.Winter Chilling and Frosts
The hard frosts of a Central Otago winter do not seem to affect the exposed buds on stems grown last year shoots. However some damage can be done on the very tips of these stems ends with no flowers being produced on that part.Rainfall and Irrigation
Viburnum are not affected directly by rainfall at any stage of there growth. However, rainfall can lead to problems with fungal and bacterial diseases if these are not managed properly.
If rainfall is not sufficient over the growing period supplementary water should be added, especially as the stems begin to lengthen. T-tape or drip systems should be used to prevent wetting of the foliage and possible disease problems.
Like most flower crops, shelter from the wind is essential. This can take the form of natural tree shelter or artificial shelter using wind cloth. A good rule of thumb when designing shelter is to multiply the final height of the shelter by 5. Use that measurement as the distance you position your shelters apart. For example, when using 2m high windbreak cloth, you will need shelters every 10m. Some consultants are recommending a multiplier of 10 for crops, but with a valuable crop such as this, a more conservative approach is advised.
If using natural tree shelter, make sure the shelters running east-west are deciduous. This will allow sunlight into the blocks in the winter. Position all shelters at right angles to the prevailing winds. Talk to your local nursery when deciding on the right tree type for your property. They may also be able to help with design.
It is especially important that the wind shelter works during the flowering season in the middle part of the season. Viburnum stems are especially vulnerable to rubbing and because the flowers are white any damage shows up very easily. Marked stems and flowers are un-saleable.
Like most flower crops, the key physical requirement of the soil for Viburnum is a relatively free draining root zone. However they have been grown successfully in many less than ideal conditions. The downside of this is potential for shorter stems which will devalue the crop.Fertility
Viburnum are a very hardy bush that do not have a large nutrient requirement. A general fertiliser such as Nitrophoska Blue is ideal applied once a season, preferably in the spring. More detailed amendments can be added based on results from a soils test and expert recomendations from a consultant.Weed Control
Weed control in Viburnum blocks is important for two reasons. Firstly it allows easier access to the plants for activities such as spraying and harvesting. Secondly, by reducing the about of vegetation around the Viburnum you reduce the potentials for weeds to host pests and diseases.
Weed control can be achieved using three means. Pre-emergent herbicides can be used successfully in some cases. Post emergent herbicides are also common provided care is taken around the crop plants. Things such as spray guards and even AI (air induction) nozzles help with this. Another technique is to grow the plants in weed mat. This is relatively new, but is showing promise.
The Viburnum talked about in this datasheet is Viburnum opulus sterile or the Snowball tree. Other viburnums are also showing some promise such as Viburnum nottcut, which is grown for its attractive berries.
Although these plants are hardy, care must be taken to watch for fungal and bacterial diseases, specifically Pseudomonas. This can be controlled firstly by pruning out infected tissue and secondly by spraying the bushes with copper before the flowers form and then as leaves start to drop off in the autumn (contact your spray professional for more information on this). The only major insect pest that has been observed on the plants is leafroller. Simple insecticides are useful to get rid of this as there is a zero tolerance to these insects when exporting flowers.Layout
Viburnum can be planted in a number of ways. The most popular is as a single plant approximately 2-3m apart. Another way is to plant them in a hedgerow situation with approximately 1m between plants. If planted this way each bush should be pruned back to only 15-20 flowering stems per season.
The first goal should be to prune the plant low to the ground. This promotes string vigorous upright stems with little or no bend in them. The best time to start this process is immediately following flowering in the spring. All stems that have not been removed in the harvest should be cut back to buds as close to the ground as is practical. From there the plant will start sending out straight stems.
A visit in January or February is recommended to remove any straggly stems or those that are growing too close together. Aim to have about 20-30 stems per m2 when the plants are mature. They will continue to grow for the rest of the season before loosing their leaves and over-wintering as bare sticks. In spring they will start growing again, first producing leaves, and then flowers. Near to harvest go back into the crop and remove any stems showing sign of damage or those that will not make a harvest grade. This prevents double handling by pickers and packers and allows more room for the quality stems to grow into without being damaged by rubbing.
During the whole season care must be taken to watch for pests and disease. Keeping the soil beneath the plant free of weeds will also assist with this.
Harvesting viburnum is a relatively straightforward process as the stems are simply cut with a knife or secateurs. Getting the timing right for harvest can be difficult. People use words like ‘moss green stage’ or the ‘parsley stage’. Talk to your exporter about what is right; as it does depend on what market you are trying to get into.Equipment
Small blocks can be managed with a back-pack spray unit and general gardening equipment. Larger blocks are best managed with a small tractor unit for spraying and grass mowing etc.Returns
Three to four seasons ago Viburnum was making very good returns in all export markets. Since then however things have changed. A lot more have been planted in the past few years and prices have dropped. Returns vary between $1-$2.00, a stem with production costs between 60-80c (2003-2004 prices).
Plants are grown from stem cuttings with a very high rate of success. These can be taken in January and grown through winter with the resulting small plants in the ground after the frosts the following spring.
If you are thinking of growing Viburnum, talk with growers at your local flower Growers Group and follow this up by talking to Flower Exporters