Gentians (Gentiana spp)

How well established is this crop?

This crop is relatively new. It has been grown commercially for approximately 5 years. Commercial returns, current growers and some level of regional based research may be available to help those new to this industry.

Background

Gentians are a perennial plant grown commercially for the sale of their cut flowers. They are a demanding crop to grow well with very specific site and management requirements. However, they are in demand in the market place, specifically in North America and Europe. Japan also is a key market for this crop. Local market sales are also made but returns are less than that received at export.

Gentians come in a range of blue colours with some whites and purples. Breeding programs are well advanced that will see the release of red and yellow gentians. This is a very positive step forward for the industry. Gentian growers can expect there first commercial harvest to occur in year 3 with full production being reached in years 5-6.

Winter Chilling and Frosts

While no figures have been published on the winter chilling requirements of this crop it appears most areas of Otago do have enough chilling to ensure flowering.

Frosts do not traditionally affect Gentians as they are dormant beneath the soil at that time. However late frosts can affect flowering buds and distort stems.

Rainfall and Irrigation

This crop needs irrigation. If the plants dry out there is a strong chance they will die. The roots like to be kept moist at all times but not wet. The type of system that is used varies between growers. Drip and tape systems are ideal. Take care with overhead systems as wet flowers and foliage can lead to an increased chance of fungal diseases.

Wind

Like most high value 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 plant 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.

Soil

Having the correct soil physical aspects is essential when growing Gentians. They like a very free draining soil with high levels of organic matter. Do not try growing Gentians if you have a clay soil. Impeded drainage will lead to high levels of plant death. Even if your soil is free draining it is best to grow the plants on raised beds to reduce the chance of water-logging around the crown of the plant.

Fertility

Gentians have very specific soil fertility requirements. If you do not get this right the chances of successfully growing this crop are almost zero. Expert help in this area is recommended. The best person for this is Alex Smith. See the contacts section at the end of this sheet.

Weed Control

Weed control in Gentian blocks can be done two ways. Agrichemicals are not recommended as they can have serious consequences on the plants.

Using black weed-mat with holes cut in it for the plants to grow through, is the most common method. This system works well and has up to 10 seasons of affective weed control. Hand weeding is still needed around the crowns of the plants but the rest remains weed The drawback from weed-mat is the increase in soil temperatures, the need for extra irrigation water and the potential to build-up soluble salt levels around the feeder root of the plants.

Some growers have used sawdust as a weed control method. This gets around the issues of water loss by reducing the temperatures and subsequently lowers the chances of soluble salts building up. The down side is the potential to tie-up nitrogen, with associated plant health issues.

Varieties

Sourcing plant material can be a little difficult for the new Gentain grower. At present the growers recommend the following selections for Otago; Ashiro Early Blue, Ashiro Mid Blue, Southland Flowers Ltd Early Blue, Southland Flowers Ltd Mid Blue. Some other selections including Southland Flowers Late Blue and some pinks and whites are available, but they do not appear to be strong producers when compared to those mentioned above.

The red and yellow varieties mentioned earlier in this datasheet are not available at present.

Pests and Diseases

When you put young Gentian plants in the ground they come in a peat plug. This could be infected with Scarid fly larvae which feed on plant roots. The traditional way to get rid of this is to keep the plugs drier. However this does not work with Gentians as the roots cannot dry out in any circumstances. The best methods seems to be to cover the whole plug with at least 5mm of soil when planting.

Bird damage of young plants is another source of concern with no really affective method of controlling them. Birds like to peck at small plants when looking for worms and other insects. Nets and reflective bird scarers, is an option but success can be limited.

Bees are another problem as they like to burrow into the flowers before they open. It is illegal to use insecticides to kill bees so control is effectively impossible.

Other insect pests such as leafrollers and thrips can be controlled with effective insecticide programs.

A number of diseases full range affect this crop including Fusarium, Pithium, Rhizoctonia and others. These are found as root rots and crown rots. Fusarium is the most common of the diseases. Chemical control is the only option.

The leaf bronzing is another problem with Gentians. This is caused by nutritional imbalance and some research work is currently being done to remedy the problem. This is looking very positive.

Layout

Gentians are planted in beds traditionally 1m wide at a density to 9m2. Beds can be as long as is practicable. Distance between the beds is usually enough to get access down. This may take the form of a 4x4 motorbike or small tractor for spraying, or if the block is small it could be less space if a back-pack spray unit is used.

Two three layers of FloraNet are used to hold the stems upright. Without this the crops will fall over and be worthless. This adds to the cost of setting up a Gentian block.

General Management

Gentian plants start growing in the spring from dormant crowns. The stems grow up through the FloraNet and are ready for harvest just after Christmas in a normal year. During the growing season they need to be sprayed for fungal diseases regularly and weeds must be controlled around the crowns. Care should also be taken to look for insect pests during the period leading up to harvest. Nearly all insects on Gentians are a quarantine pest in importing countries.

At least 5 stems should remain on the plants after harvest to ensure the plant can store enough carbohydrate in the roots to grow again the following year. As the plants die down in the autumn they are cut back for winter with the dead foliage being removed from the block and burned.

Harvest

Harvesting Gentians is a relatively straightforward process as the stems are simply cut with a knife or secateurs. Another way is to simply break the stems between the thumb and forefinger. The difficulty is then removing the stem from the layers of FloraNet that are holding it up. They are traditionally cut straight into water and then put in a post-harvest solution back in the packhouse. The stage of cutting depend son the final market. Export stems are cut when only 1-2 buds are open. Local market stems can be a lot more open than this.

Equipment

Gentian growing can be as high or low tech as you want it to be. The size of the block is the best determinant of this. 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

The traditional rule with the returns from a Gentian crop was 1c for every cm of stem length i.e. a 70cm stem will return 70c. This rule still works in most seasons.

Establishment costs have been calculated to be as high a $24/m 2. This includes plants at up to $2.60 each and the costs of posts wires floranet etc. The first export harvest is made in year three with full production being reached in years 5-6.

Contacts

One of the most knowledgeable people on the growing of Gentians is Alex Smith of the New Zealand Horticultural Advisory Service Ltd. He can be contacted on 03 3324945 or on e-mail advisor@nzhas.co.nz