Tag Archives: polytunnels

Biological warfare

With a cold wet summer such as we’re experiencing this year it can be a bit of a relief to go down to the polytunnels where it’s nice and dry and we have much greater influence over the growing environment. These warmer conditions can bring problems of their own, however, as what is good for something like a cucumber can also be good for pests such as aphids and red spider mite, which can rip through a crop if nothing is done about it. Aphids have a life cycle of 3-4weeks (depending on climatic conditions) and during that time can give birth to 40-100 live young who emerge with the next generation already inside them!

Some predators will follow these pests through the doors: ladybirds, lacewings and hoverflies are all welcome visitors and we have some plants dotted around to encourage them (lacewings love fennel, for example) but this isn’t always enough and so we boost their numbers by distributing extra pest-specific, insects and bugs through the crop.

These fall into two main categories: predators and parasites. Predators (like phytoseiulus persimilis for red spider mite and aphidoletes aphidimyza for aphids) will attack and eat the pest, then lay eggs which hatch into a new generation to continue the process. Parasites are, if anything, more gruesome: aphidius colemani, for example, will lay an egg inside the aphid itself. This obviously kills the pest as the larva grows and when it hatches, carries on the process. Parasites tend to be much more host-specific than predators, which aren’t too fussy (within reason) what they go for. In both cases, the second generation tend to be more active and vigorous than the parents we introduced as they are more acclimatised to the conditions in the tunnels.

Some battles you win and some you lose: to date there are no signs of red spider mite, but our peppers have a few green aphid and one of our cucumber tunnels is fairly heavily infested with black aphid. We have ordered extra insects to help in the war and I have even been introducing the odd ladybird I have found in the fields! Hopefully this will be enough and we can get on top of the problem.

ImageBack outside, meanwhile, we are beginning to harvest our globe artichokes. These highly architectural plants, a relative of the humble thistle, are one of the many crops to have taken a bit of a battering from the elements: they can suffer from browning leaves if conditions are too humid but are worth persevering with as they’re relatively low maintenance for a perennial crop and have a great and unique flavour. I tend to just steam them and eat as a starter with loads of melted butter, though I’m sure Rob in our Field Kitchen restaurant has far more imaginative uses for them…

Ed’s Farm Blog – Springing into inaction

wet garlicOur early season crops are usually planted in fields across the valley from us, as they are broadly southfacing and warm up quicker with well-drained soil to allow early planting. As these can’t be irrigated we rely on the usual April showers to water them for us. Last year the long dry spell actually meant that some of the lettuce got stressed, bolted, and we lost a fair amount of the crop. Not this year! Below average temperatures mean that the crops are growing more slowly than hoped, but there is certainly no lack of water.

Continual rainfall such as we are experiencing at present brings its own set of problems, however. At this time of year we would be frantically planting, fleeceing, brushweeding and hoeing our lettuce, spinach, summer greens and so on; but not now. The fields are simply too wet to cultivate and a short break in the weather is little help as they need a minimum of 2-3 days (sometimes more depending on the soil) to dry out enough to work.

Fortunately for our staff there has been plenty to do in the polytunnels: Manuring, putting up supports for tomatoes, and plenty of hand planting. But as this begins to draw to a close we can forsee a few quiet weeks ahead whilst we wait for the crops we have to come on and pray for a break in the weather.

On the up side our wet garlic is looking good; this was planted as individual cloves that we broke up from whole bulbs in late October and early November. The two varieties we grow are Germidor and Messidrome as they produce large cloves: and usually the larger the clove you plant, the larger the wet garlic you produce.

So a mixed spring so far. To quote the philosopher from Morecombe, “bring me sunshine…”

Ed’s Farm Blog – loo roll in the polytunnels

Ed's Farm Blog - Organic SaladI’m Ed Scott, and I work on the Riverford Organic’s founding farm in Devon. The plan is that I’ll be writing a regular farm blog, showing you what we’re growing and how we’re growing it.

It’s now the beginning of February, and we are busy picking leeks and the last of our curly kale from the fields. We have also just laid the last of our winter salad pack in the polytunnels. The majority of our salads are block-planted through a plastic mulch, and treated as ‘cut-and-come-again’ crops; these can be picked between three and five times, dependant on type and variety.

As well as the blocks, a proportion of our salad leaf plants come in seed matting; a large spool of seeds sandwiched between plastic and a blotting-paper like material. Much like cress grown on loo roll at home, upon germination the roots reach through the paper into the soil below, while the leaf pushes up through tiny slits pre-cut in the plastic. This system has the advantage of lower plant and planting costs whilst ensuring the crop is not swamped with weeds; and although we have mixed feelings about the volume of plastic used, it’s actually no more than that used in our traditional block planted system.

TEd's Organic Farm Bloghe disadvantage of this system is that the seed matting doesn’t work with all plants and can only be cropped once; our first planting went in during October and was harvested in the run-up to Christmas. The rolls laid this week should be ready for harvesting in late March. Keep an eye out for further pictures showing progress through the growing stages.

Ed Scott
Assistant Harvest Manager

Strawberries and plastic: are tunnels worth the eyesore?

Over the last twenty years the huge majority of the UK strawberry crop has moved from open fields to the protection and intensification afforded by hundreds of acres of polytunnels, largely in Kent and Herefordshire. Plastic can advance a crop by perhaps two weeks, but the great advantage is the protection it gives from the vagaries of a British summer. Fruit must be picked dry to avoid bruising and to give a reasonable shelf life. Even more importantly, persistent dampness leads to a build-up of fungal disease, particularly botrytis, which can reduce a good berry to a foul tasting pulp in a matter of hours.

Our strawberries are grown extensively on high ridges at wide spacing which, in a normal year, gives enough airflow to dry dews and rain before botrytis sets in. There can be no doubt that polytunnels are a blot on the landscape; the question is whether they are justified by the economic and environmental benefit they bring by reducing wastage, extending the UK season, excluding exports and thus reducing food miles. For twenty years I have stubbornly persisted with growing outdoors, with the result that we have a relatively short season and, over the last few years, have not been able to pick up to a third of the fruit. Initially I was convinced that growing outdoors gave better flavour, but now I am not so sure and wonder if I have been overly dogmatic in my resistance. Across the five regional farms we would need eight acres of tunnels to provide a good supply of strawberries for the 45,000 homes we deliver to each week. Your views would be welcome.

Guy Watson