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Hydroponic herbs
Moolman says they currently have 31 hydroponic tunnels plus a net house . Some herbs are grown on a 1 , 8 ha open field . Herbs grown include rocket , wild rocket , coriander , mint , curly parsley , Italian parsley , French chives , dill , thyme , rosemary , sage , oregano and various micro green vegetables and herbs . Around 1 , 5-2 tons of herbs are harvested every week .
What herbs are in “ in ” right now ? Moolman says people are going crazy for mint and she recently had to convert a further tunnel for mint cultivation . “ We believe it is a trend related to the popularity of the Banting diet . People may use mint to flavour their water and teas .”
In general South Africans are consuming more herbs and Moolman comments that their increasing orders show this trend .
“ People are becoming more aware of eating healthily and using fresh and seasonal ingredients in their cooking . TV cooking shows and contests are also very popular at the moment and people are inspired by them and eager to try the recipes at home ,” she says .
Structures and design
The Allée Bleue tunnels are all Vegtech2000 structures . Moolman elaborates on the structure and design for us . The tunnels are :
• 10m x 30m structures covered in super diffused plastic .
• Open in front with netting at the sides to help with ventilation .
• Fitted with plastic curtains and doors , which used to control the ambient temperature and humidity inside the tunnels
• Orientated to face the South East wind head on so if the wind picks up “ we close the south east side . In winter we close the North West side when it rains to protect the crops from the rain coming in .”
In general , the hydroponic systems and protected environments ensure good quality crops and there are several benefits of the systems , explains Moolman .
“ We grow herbs hydroponically to ensure good quality of herbs for our customers as well as consistency in supply . Because the herbs are grown this way we can supply the plants with all the water
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and nutrients needed in the right amounts . The medium can be managed to ensure the roots are happy and conditions in the root zone are good for growing .”
Plants grown under protection are shielded from the harsh sun , observes Moolman , and protected from the wind and rain . “ Their leaves are much softer and free from bruises . Inside the tunnels the plants ’ roots are much warmer than it would have been outside , which means the plants will grow much faster than when it has cold feet . Also , because the herbs are grown in coco peat the leaves are relatively clean and free from sand .”
Interestingly , Moolman says that coco peat is actually a byproduct in the coconut industry . There is a fascinating history behind this medium .
“ After factories have extracted the long fibres off coconuts to make products like ropes and mats , you ’ re left with a fine pith , the coco peat . These factories used to leave the coco peat in giant heaps and burn them after a while , if they ran out of space . Due to the amount of coco peat that was generated one of these companies sought a use for this waste material in horticulture . Trials proved very successful - as coco peat has excellent water holding capacities , contains a lot of oxygen and anchors plants really well .
“ So now coco peat heaps are left to compose for approximately 3 years , then sterilized , dehydrated and compressed into blocks for easier transport . This is a great substrate for herbs and leafy crops , but requires close management . Coco peat holds water very well but it can also hold nutrients and lead to salinity problems .”
Humidity
Ventilation is an important factor in tunnels . One needs to keep an eye on humidity , if you are an entrant to tunnel farming .
As Moolman puts it : “ Tunnels can be much more humid than an open field which can be detrimental for herbs as high humidity can lead to plant diseases such as downy mildew - so it is important to ensure good ventilation in your tunnels . A lot of novice or new growers tend to keep their tunnels closed during periods of cold temperatures , but it is far more important to have good ventilation .
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“ The little heat you manage to build up by keeping the tunnel closed is not worth all the problems you create by increasing the humidity . Rather have your plants cold but dry ! Depending on your crop , it is not always necessary to heat the whole greenhouse . If you can just warm up the root zone , by using mulch for example , you are half way there and the plants will grow much better .”
Irrigation and fertigation
Close monitoring and careful management is vital . Moolman says that the irrigation and fertigation water that is applied to the medium - and especially the run-off water that comes out the medium - must be closely monitored to make sure that the plants are using the nutrients you are feeding them and any excess is draining freely and not building up in the medium .
The herbs are irrigated and fertigated with a NMC PRO Irrigation System from Netafim . Dripper lines deliver the fertilized water straight to the root zone and overhead misters are used to cool the tunnels down during the summer months . The herbs are irrigated 4 to
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5 times during the day in summer , with an additional cycle during the night time . It is more difficult for the plants ’ roots to absorb calcium in summer , says Moolman .
“ Therefore so I give an extra cycle with calcium only to make sure the roots can absorb the calcium without it having to compete with other nutrients . In winter I only irrigate the herbs once or twice a day , but I give a much stronger EC than in summer .”
Water conservation
Does this herb farmer believe greenhouses help to use water more efficiently ? Indeed , she says , at Allée Bleue the careful management extends to good care of the precious water on the farm .
Comments Moolman : “ Greenhouses do help to use water more efficiently because you can control what goes in - and manage what goes out . With the troughs I use for the herbs , I make sure that I have a 10 % leach of water , anything more than that and you ’ re wasting precious water and fertilizer .
Only borehole water is used for
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