An early start?

English growers are probably as confused as their plants by the weather they are currently experiencing.

Our rivers have flooded and there have been VERY few frosts. A meteorologist told a recent grower conference that the jet stream and storm track have been sitting on top of each other for much of the winter, a fact that probably explains why most of the contents of the Gulf of Mexico has ended up in our fields.

Another rainy day at Haygrove Ledbury

In some countries growers are worried about leaving strawberry plants in situ for the winter because of frost kill whereas in the south of England, this year, our plants may not have accumulated optimum chill units under tunnels in some districts. We may regret not having left them outside! Having said that, it is important to understand that although it hasn’t been freezing, it hasn’t been warm either so some of the chill totals are higher than growers might have feared.

There also concerns that where new frigo plants have been planted into coir bags, they may be making top growth in the mild conditions but not developing sufficient root.

Oh well…… At least it was sunny today!

I will go an drink a glass of wine from last years tunnel crop – see below - and remember what warm weather feels like.

Wine grapes protected by tunnels








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Autumn Harvest


Corn at harvest, England

Growers in Britain can feel the autumn coming, on some nights
it has been very Autumnal. Apple growers
would like some good day-night differentials to accelerate fruit colouring but
berry growers are probably keener to accumulate as many growing degrees as possible
because they all add up to extra yield.

Knowing that our North American cousins refer to the autumn
as ‘fall’ – which makes a lot of sense – is a reminder that we hope that fruit
prices will do exactly the opposite at this time of year. Unfortunately prices
haven’t been so good in recent Septembers with the late crop of glasshouse
strawberries clashing with field grown day neutrals. We are not sure what this
September will bring – some day-neutral varieties were badly hit by a British
heat wave in July. That is several days above 30oC here, so nothing
very exciting for most fruit growers in other countries, but enough to cause some
UK adapted varieties to go into a kind of exhaustion.

Tired leaf = tired plant and probably no flower coming

However some other varieties are looking fantastic right
now. If we can keep botrytis out so that picking can be extended well into
October, many growers will have a good Autumn.

A late everbearer variety - pushing a lot of fruit for September on table tops


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Physiological Confusion

Too hot for an Englishman but what about strawberries?

A physiologically confused Fruit Doctor is writing this
item: Having spent time in the Yarra Valley in Australia at 37oC at
the beginning of March and last weekend in Scotland admiring the snow capped
mountains but worrying about the likely impact of a late season on the UK strawberry
market. Isn’t it amazing that we can grow berries in such diverse environments?


In Australia the light is so intense that ripening strawberry
fruits are often scorched in the field before they can be picked. Growers have
found that diffusing poly films can prevent this scorching so that even in
temperatures above 30oC they are reluctant to vent. This contrasts
with standard practice in Britain where strawberry and raspberry growers are exhorted
to avoid more than two hours per day above 25oC, venting to avoid
such events.


Sun scorched strawberries

The University of California bred strawberry variety ‘Albion’
has now been grown successfully by growers at farms ranging from Aberdeenshire,
Scotland to Victoria, Australia. Wow!


A slow start to Spring (England, on the official first day of Spring 2013)

If there are problems, these are often the result of
variations in humidity (low and high) or raised night temperatures. Measuring
these variables and understanding their effects is important because it isn’t
just variations in temperature that cause physiological problems in plants.


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Season Starting!

British growers have been skinning tunnels for some weeks
now. A few growers skinned in the first days of January or kept the tunnels
covered for the whole of the Winter after adding some strengthening systems
(ranging from bracing wires through to steel tubing or even the new Gothic
shaped hoops). We have been coping with almost continuous precipitation until
recently but the rain turned to snow in January.


Growers who had already skinned were able to use available
labour to get on with planting and other tasks whereas at other sites, people
returning to work after Christmas, often from abroad, were faced with a
frustrating and expensive wait for a gap in the weather. While skinning early
remains a ‘calculated risk’ we have become more confident both in our
understanding of how to specify tunnel structures and in our management of
those structures once built.

Clery coming into flower, Cornwall UK, 3rd week of February


Right now there are some open flowers on the early June
bearer variety ‘Clery’, down in Cornwall under fixed tunnels over fleeced table
tops whereas outdoor fields in Herefordshire have hardly moved. Most of the
early fields now have tunnels with doors and the crops underneath are protected
by one or two layers of fleece (USA = “row cover”) or a layer of fleece plus a
layer of perforated clear film.


But…. that doesn’t mean they can be ignored! Agronomists
will be crawling around under the fleece, looking for aphids and it won’t be
long before the crop needs ‘managing’ again. Fleece and the perforated film
heats the crop but cuts out a lot of light. If left on too long or if tunnels
aren’t vented during sunny weather plants become ‘stretched’. The foliage
becomes leggy and soft, collapsing easily later on.


For outdoor crops a week in May is worth more than a month
in February for growing degrees (see table below, for 2012) but under well sealed tunnels things will happen much faster. 2012 was a strange year for British growers because April was colder than March!

UK growing degree hours, Spring 2012


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A visit to an impressive HAMK University of Applied Sciences school at Lepaa, Finland.

Raspberries under Haygrove Tunnels

The school is well equipped, even boasting a micro-propagation facility, and filled with a great bunch of students. I was fortunate in meeting a young grower, albeit no longer a student, who managed to grow 1.4 kg/cane of fruit from cold stored long cane raspberries imported from England (!!).

The Finnish consumers are said to prefer the flavour of more traditional varieties but these are grown because they have proven their ability to survive the near-arctic winter. However Glen Ample is also finding a good market. Tunnels are, of course, essential for growers who have chosen to invest in such expensive plant material.

On the subject of the arctic: It is worth reporting that we also met Pauliina Palonen, a widely respected small fruits researcher. Pauliina is currently working in a team trying to improve the stock and growing techniques of the arctic raspberry or nagoon berry (Rubus arcticus). This fruit has a remarkable, aromatic, flavour and is bought for use in drinks. It is exciting to see this kind of work: How many new or half forgotten fruits are waiting for an innovative grower to find?

Arctic Raspberry (source: Wikipedia)



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Focus on Light

Fruit Doctor attended an excellent event, entitled FOCUS ON LIGHT SPECTRUM at the Stockbridge House Technology Centre here in England on Tuesday of this week. The meeting kicked off with an excellent presentation by Professor Nigel Paul (Lancaster University) and included talks by several leading European researchers and finished with talks by three growers who have been pioneering polythene tunnel covers that exert special effects on the spectrum of light for the crop or with new generation LED lamps.

Much of the discussion was focused on the development of crop and variety specific light recipes to optimise the use of LED lamps but another important strand was the effect of ultra-violet light.

It seems that there are no UV generating lamps for commercial scale horticulture (hectares) on the market so the only way to raise the amount of UV reaching a crop is to change the type of glass of poly used to clad the production unit. The ultra-clear teflon related material known as F-Clean was discussed. F-Clean was the material chosen by the famous Eden Project here in the UK.

Conventional greenhouse glass and tunnel poly allow very little UV to the crop but UV has been shown to boost flavour, enhance fruit/leaf colour and encourage the production of a more compact plant.

Standard and UV window light transmission spectra

Fortunately for tunnel users a generation of UV ‘window’ films are available. Look out for Visqueen Lumisol, for example.




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Wrapping up for Winter

I think that anyone reading this will be feeling some
sympathy for our American friends who may have been affected by Hurricane
Sandy. It’s risky enough being a grower without “Super Storms”.

Frost damaged Elsanta strawberry crown after Winter 2010-11, UK

Growers of table top strawberries face a particular  challenge if they decide to over-winter a crop instead of replanting in the Spring. The compost filled troughs, pots or bags are exposed to un-relenting  chill if left on the table structure.

There is no moderating effect of the surrounding soil – something that prevents severe crown injury in conventional  fields in all but the coldest districts.

Furthermore, any blanket of snow does not  prevent heat loss from beneath the containers. In Britain, growers are advised  to move containers off from tables and onto the floor if night temperatures below -8oC  (46oF) are expected.


Roots of Elsanta plants damaged by a combination of freeze injury and phytophthora

This is expensive on labour and exposes the plants to soil borne pests and diseases, perhaps especially Phytophthora fragrariae. If the plants are then covered with fleece, Botrytis and aphids can be difficult too.

Possible Solutions

  • Wrap the containers in fleece (row cover) in situ. This has limited benefit if
    freezing conditions persist for many days.
  • Convert to 4-season tunnel structures. Under a
    tunnel the wind chill factor is massively reduced and fleece is easier to
    manage. Maybe a heat source can be made available for extreme events.
  • Haygrove have developed a patented telescopic
    table top system so that tables can be lowered and raised quickly.


Telescopic substrate system, Autumn 2011, in the "up position".


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Heading into the Winter?

Having returned from a Haygrove meeting in Pennsylvania –
where day time temperatures were still in the high 20s (Centigrade) England
feels like a tough place to be growing anything. We had a 2oC night
at the weekend which caused pears to drop of the trees prematurely. When it’s
not cold, it’s dank and humid.

Need to vent!

At the meeting in America we discussed the management of
managing both temperature and humidity, focussing on Vapour Pressure Deficit (VPD). The only way to get this
right is to vent a lot at this time. If we don’t close the tunnels at all we
lose the extra growing degrees (and yield) we want so auto-venting is the smart

Better venting!

And then the weather gets really cold and growers with table
tops have to decide whether to keep tunnels skinned or to move the bags onto
the ground….. More on the solutions we discussed will follow.

If you aren’t heading into Winter then you are in the
Southern hemisphere – have a look at the Haygrove South Africa blog:

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Northern, temperate zone berry growers are busy with tunnel doors at this time. In England some have belatedly decided to install temporary doors now that the weather has changed. We had Californian weather for March but we have moved back to the Arctic for a spell now. A Californian academic commented on the radio this week that “What the British weather giveth it also taketh away”. Growers of oudoor crops are wondering what it ever gives them as we see a -3oC frost forecast with pears and apples both coming into bloom.

Scottish growers had weather that was as warm as mid Summer last week but many centimetres of snow this week! Away from the most extreme winds of snow this weather is annoying for tunnel growers but not dangerous…. but what to do about doors?

Unless the location is very sheltered, Haygrove recommend Streamline doors for temporary and fixed tunnels where extreme earliness is required. Withstanding strong winds these doors and adding to the structural wind resistance of tunnels ends, Streamline doors provide 100% sealing.

Most berry growers growing under 4-Series type tunnels on temporary sites opt for simple, low cost doors of the type shown in the image below. Makes sense…. cheap, quick to install etc.


Simple door, in open position (tied back to hoop)


….. But the climate is never right and every time the weather changes the grower must decide whether to spend money on labour, opening or closing OR lose yield or quality by compromising on the growing environment.

By far the best doors for field scale tunnels are ‘roller doors’. Unless the tunnels ends are staggered instead of straight of swept, roller doors can be set up to open several tunnels at once. Haygrove Farm now has many blocks kitted out with roller doors and for semi-permanent substrate fields the doors are now motorised. The new table tops have both doors and roller vents linked to climate sensors. Now we can concentrate on the plants and not the labour cost! 


Roller vents controlled by climate sensors

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No Rain……In England???

Here in England we are finding ourselves short of water. That will come as a big surprise to growers from warmer countries.

Having said that I note the following ‘facts’ from Wikipedia at


Highest amount of rain in one year = 26,470mm (Cherrapunji, India)

Average annual total rainfall = 11,872  (Mawsynram, India)

Most rain in 12 hours = 1,144 (Foc-Foc, Reunion)

Most rain in 1 hour = 305mm (Holt, Missouri)

However much people complain about British weather, we appear to be pleasantly dry by world international standards and now un-pleasantly dry for strawberry growers!

At our British Haygrove Open Days we discussed water conservation and erosion control. We based our calculations on an average rainfall of 792mm (for Ross-on-Wye, Herefordshire) but also presented calculations based on provisional data for 2011. I was shocked when speaking to a leading grower and nurseryman from the East of England, to find that he had recorded only 100mm of summer rain. I have subsequently discovered that the April-August total for Ross was actually a similarly low figure (97mm).


Annual rain fall April – August (incl.)
Ross-on-Wye (average) 706 248
Ross-on-Wye (2011) 522   97
Watsonville, California (average) 582 60

Figures from:

Average = 1971 – 2000

We were demonstrating a mobile steel gutter forming system and calculating how much the water collected from guttered fields, during the covered season, could contribute to the total need of the crop. Allowing for the fact that, due to evaporation, only about half of the rain landing on a tunnel would be collected by the gutters we calculated that in a relatively dry year like 2011 we could collect 25 -30% of crop need. In a normal year the number would between 45 and 75% of need.

Haygrove Guttering System

Haygrove Guttering System

In the UK ‘mains’ water can cost commercial farmers £1.30 per m3. Water from the gutters could therefore save £1,300 and £2,000/ha. The collected water is also largely free of salts – great for salt sensitive crops and for diluting saline water supplies.

Statistics from Mark Else at East Malling Research ( show that a commercial crop of soil grown strawberries requires around 70 m3 irrigation water per tonne of harvested fruit. With some sophisticated sensor equipment it is possible to make substantial reductions in irrigation requirement. East Malling has suggested a target of 10m3 per tonne although the industry has yet to see whether this will sustain the consistently high yields it requires to remain competitive.

Even though table top and glasshouse systems are completely dependent on a ready supply of water the high yields achieved tend to bring the water use per tonne significantly below the 70m3 average.

For me it is clear that growers will be investing more in soil moisture sensors and decision support systems but I also foresee a big increase in gutter installations both to collect water from the roof and to collect drain-water from soil-less growing systems. It is likely that many growers will also be forced to re-cycle/re-circulate that water.



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