Cherry flower, Haygrove Farm organics 2010

Even as early as December English strawberry growers will be planting cold stored plants that have received enough chilling and glasshouse salad crops will be taking delivery of new plants for early, heated crops. Both these will be have consider pollination very carefully and will be using bumble bees.

Some important points to remember if you are planning to seal up your tunnel or glasshouse for maximum earliness:

• If the structure is sealed to retain heat (or to exclude insects) pollinating insects will need to be placed on the inside or flowers pollinated by hand
• Bumble bees are best for pollinating early crops. They are not aggressive and fly at relatively low temperatures.
• Don’t forget that, if the sun comes out, temperatures in a sealed structure will rocket upwards. That will cause bees to retreat to their hive, on fanning duty, to protect their brood and will also mean that your plants are use more energy respiring than they make photosynthesising. For most crops its not a good idea to let the air temperature rise above 25 degrees C.
• For small structures its usually best just to leave the door open and let local bees and other nectar feeding insects do the pollinating. For tomatoes many growers appear to find that their own business and some air movement provides pollination.

More recently temperatures jumped upwards, taking apple growers by surprise as buds moved from very early bud break to the mouse ear stage within a few days. As is typical of the British climate, the warm air brought rain too leaving many growers ruing missed opportunities to protect orchards from scab, before the inevitable showers arrived.

With the temperatures rising, early strawberry tunnels also came into flower. For the earliest of these, first flowers appeared in the week leading up to 25th March. Even though the cold returned last week, pasture has greened up and there is evidence of Spring everywhere in the South.

It is surprising that there is still discussion about the most effective way to bring on early strawberry crops under tunnels when it seems so obvious in the field!

GOOD SEALING + FLEECE + FLOATING MULCH

In the other countries fleece = ‘row cover’ and floating mulch = “perforated film” or “perforated poly”

When temperatures dropped last week well sealed SOLO tunnels remained warm and when the strong winds hit us at the end of the week growers were able to keep them closed, especially when fitted with STREAMLINE doors.

To avoid damage from Feb-March winds the safest option is to delay tunnel skinning and rely on ‘fleece and floating’ alone or to choose stronger tunnel designs such as the SOLO (with 2mm wall steel).  In Britain the best money still comes from early crops so, for strawberries the industry is gradually moving towards much stronger tunnels.

Krzysztof Wiesiolek digs down to his blackberry canes under snow over fleece.

For growers who have been able to find an export niche and/or extend the season using tunnels or new varieties Poland is an exciting place to be, despite what are sometimes extreme and unpredictable weather conditions.

Creating a large more stable air volume under tunnels during the summer, without sacrificing earliness, is a challenge. Haygrove’s Marek Jamry is enthusiastic about the high, ‘fixed top leg’ or guttered Greenhouse Series. These have been proven during hot weather. It is also possible to augment the standard design with additional supports as insurance against early snow. Snow, however, remains an important limiting factor so the debate about the most appropriate hoop shape and overall structure will continue. Marek has been consistent in his advice that growers should de-skin when heavy snow is forecast.

In Germany growers have tended to prefer Haygrove Solo tunnels. These are constructed with a gap between each tunnel to facilitate venting and snow removal. The gap also leaves extra space for snow to gather without harming the crop or compressing the side of the tunnels. When vented the Super Solo tunnels provide a surprisingly large, open air space.

Haygrove Solo tunnels, Germany

Haygrove Super Solo tunnels in England. Expecting rain! Sides pulled half down to protect a ripening crop of table top strawberries

Mid Winter, Newent, UK

For northern European growers the new year is kicking off with key staff returning to farms to prepare for the coming season. In Holland there will be glasshouse growers who have only just stopped picking Elsanta strawberries but the majority of English soft fruit growers are looking at snow covered fields or frozen bags at the time of writing. Many will be wondering how to maximise returns in a tight economic situation. Yield is still key to this and were above average for many in 2009 but earliness also has a massive impact. Growers who have succeeded in producing a substantial quantity of strawberries before mid May or raspberries before mid June have probably had the best of the last 2 – 3 years. They are less dependent on growing or market conditions in the Autumn/Fall to get their businesses into profit after months of cash-flow worries.

Well built roller doors, Poland

How to get the earliest crops without artificial heating?

FAVOURABLE SITES

EARLY SKINNING/COVERING

ATTENTION TO THE DETAIL OF SEALING UP STRUCTURES TO RETAIN HEAT

These subjects may be the subject of later postings but for now it is worth noting that all the four points are closely connected.

FAVOURABLE SITES ARE OFTEN ALSO SHELTERED SITES

SHELTERED SITES ARE EASIEST TO SKIN/COVER EARLY AND REPRESENT THE LOWEST RISK WHEN SKINNED/COVERED

YOU WISH TO EXPLOIT THE SITE FOR AS MANY YEARS AS POSSIBLE – PERHAPS ROTATING SOIL GROWN CROPS WITHIN THE STRUCTURE OR INSTALLING SOIL-LESS GROWING SYSTEMS. THIS JUSTIFIES ADDITIONAL INVESTMENT IN THE TUNNEL STRUCTURES: GOOD DOORS, GUTTERS AND OTHER MODIFICATIONS THAT IMPROVE HEAT RETENTION ….. AND…. YOU ADD STRENGTH TO EXISTING TUNNELS OR INVEST IN THE NEW, STRONGER, DESIGNS SUCH AS SOLO, TRELLIS AND TELESCOPIC SO THE TUNNELS CAN BE COVERED EARLIER STILL – OFTEN COMPENSATING FOR THE DELAYING EFFECT OF SWITCHING TO SOIL-LESS SYSTEMS.

Good Sealing