March 2018

Geothermal energy is harnessed to produce thousands of gerbera flowers each week at PlentyFlora

Geothermal energy is being harnessed and used to grow thousands of gerbera flowers each week in the computer controlled glasshouse operation of PlentyFlora. Harald and Connie Esendam set up the business in 2002 (with a lot of help from friends) and sold their first flowers at the roadside at Christmas in 2002.

Harald has a horticulture degree and after graduating worked at the Research Centre for Flowers in Aalsmeer (Holland). For ten years he led a research and breeding team at Terra Nigra, a globally significant gerbera and rose breeder in Holland.

In 1995 Harald and Connie moved from the Netherlands to Rotorua, where Harald worked for Carter Holt Harvey in research, developing a research glasshouse and managing the Radiata Pine nursery at Tokoroa. Connie’s background is in administration and marketing and combined with Harald’s extensive background in floriculture, they make a formidable team.

Gerberas are a sub-tropical plant native to South Africa. It was named in honour of the German botanist and medical doctor, Dr. Traugott Gerber. Scotsman Robert Jameson discovered the plant in Barberton (S. Africa) and brought it back to England. So the plant’s scientific name is Gerbera jamesonii.

In the early 1900s breeding programmes began in the Netherlands. Gerberas have a highly complex genome, so about 100 years of breeding with Gerbera has resulted in a vast range of sizes, colours, flower-shapes, stem length and productivity of flowers per plant.

The success of Harald and Connie Esendam’s PlentyFlora operation relies on a sustainable, affordable supply of heat for the 2,688 square metres of glasshouses that produce (during the summer months) up to 16,000 blooms each week from around 14,000 plants. In winter, production drops to between 8,000 and 9,000 blooms per week. PlentyFlora produce both standard and mini gerberas, and produce 100g bags of petals as biodegradable confetti.

The location in the geothermal area near Rotorua is key to their business. The glasshouses were built in 1999 and geothermal energy is used for heating them.

Controlling the glasshouse environment ensures year-round production. Two bores have been drilled on the property with permits from Environment Waikato. They provide heat by way of a compressor creating air-bubbles at 36 meters depth to push up the geothermal fluid. This brings energy from two shallow geothermal bores. The original bore produces liquid at about 85 degrees Celsius. A heat exchange system transfers this heat to pipes filled with water that run through the glasshouses.

The use of an air-compressor has increased the flow of geothermal water from 2.5 cubic metres to 5.5 cubic metres per hour through the system, which has meant greater ability to heat the glasshouses to the desired temperature by mixing it with cool water (to about 55 deg C). The cooled geothermal material is returned to the aquifer to eventually be re-heated.

A new bore was drilled in 2007 and supplies heat (at around 65 deg C) directly to the greenhouse in an overhead system. This has a beneficial effect on the humidity around the plants in winter.

The heating system has developed over the 15 years of operation. Harald credits Ian Baldwin with providing technical support and Ian continues to provide this (on a part time basis). In the past they had to rely on a diesel oil-burner to top up temperatures in winter but today the business is 100% geothermal.

As well as controlling glasshouse temperature, a computer automates opening and closing of the windows and deployment of shade cloth, to provide shade during the day and added insulation at night. Fans are affecting humidity levels positively as well.

Plants are grown in individual pots with coconut husk as growing medium. They each have a dripper that supplies water and nutrients in a semi-hydroponic system. The pots are suspended in tables at a convenient height for those hand-picking the flowers.

Unlike roses, gerberas are picked when open. The stems are not cut but picked (to prevent transfer of any fungal disease that might be present) and slipped into protective transparent sleeves for transport. PlentyFlora pick on Monday, Wednesday and Friday to fill standing orders from around 60 customers. Excess flowers are sent to auction flower markets in Auckland and Wellington. The company also sells flowers online and at the glasshouse entrance (shop).

A staff of five (including Harald and Connie), plus two part time workers, grow around 60 varieties of gerbera. Standard flowers have a diameter of between 10 and 13cm, mini gerbera measure 6 to 8cm across. The mini gerberas were developed by Terra Nigra and have an extended vase-life (around 30%) and are popular for cakes, button-holes, hairstyling and popular smaller bouquets.

The busiest time of year is in spring, when around 35% of plants are replaced by new stock. Mono-clone tissue culture (producing exactly the same type of a selected flower) is imported from Holland via India and grown on in peat pots at specialist nurseries in Auckland for about two months until they are well rooted and ready for the glasshouse. Once at PlentyFlora, it takes another 6 to 8 weeks to produce flowers for the market.

Each plant produces flowers for around 2-3 years but Harald has a variety that is still producing well after 6 years. That is called “Proza” and is a popular creamy-white wedding bouquet flower.

New varieties are being produced all the time, thanks to the gerbera’s complex genome. One new flower is a “spider” type, with fine (folded) petals crossing over each other. “It will provide an extra 3D-effect the florists will like”, says Harald.

Harald says after 15 years of growing he is still learning. In particular, the need for constant vigilance around plant health. He has introduced beneficial fungi and experimented with insects for biological control of insect pests, although he admits it is a difficult balancing act. Harald says there are few beneficial insects that are available in New Zealand for biocontrol in the glasshouse, and each require specific environments that can’t always be met, so some spraying is necessary – although more use of biological control is still a goal for him.

Being located on the Central Plateau at 300m above sea level means humidity (and therefore fungi such as botrytis that causes grey mould) is less of an issue than for glasshouse growers located further north. Close targeting of spray management also cuts down on the amount of spray required in the system. The sprays used are less toxic and more oil-based than they were in previous years.

In 2013, PlentyFlora won the Holland Beckett Manufacturing & Trade Award and was a finalist in the Westpac Rotorua Business Excellence Awards. Harald says the experience made them take a closer look at the strengths and weaknesses of the business, which has allowed them to grow further.