Sunday, 1 June 2014

Growing fruit under cover - getting the most from a Poly-tunnel

For those with the luxury of their very own Poly-tunnel the sky is the limit for exciting new possibilities with regard to growing fruit and fruit culture.
The protected and controlled environment and extended season inevitably excites the imagination and possibilities. To maximise this potential some thought should be given as to what to grow.
Not all fruits would represent the best utility of the available space; to qualify for inclusion it should satisfy any one of three criteria:
To require or perform better in a warmer/protected environment.
To have the ability to provide an extended season compared to outdoor grown examples.
To benefit from bird protection.
So, if you were thinking of growing gooseberries, or blackcurrants or blackberries for example – well then of course you can, there isn’t really anything in the world of fruiting plants that won’t grow under cover – but my advice would be don’t because they do not particularly fall into any of the above categories and would not represent the best use of space. So what should you grow? Here’s some recommendations…..
The renaissance in commercially grown cherries can be attributed to them virtually all being grown under cover these days. Precious few of the old original Kentish Cherry orchards exist nowadays. It is because the Cherry yield in this country was just too irregular in weight of crop and quality to satisfy the requirements of a commercial supply. But, following the lead of European Cherry growers, virtually all commercially grown Cherries are now grown under plastic cover, either permanent or temporary. The results are startling. Increased yield, better quality and better flavour and a far more consistently reliable crop. It is protection from late frosts that may harm the flowers, high winds, which strip branches of immature frits, and heavy rain which can mark or make the fruit split that is of such value. Of course with the restricted availability of head room consideration must be made as to the eventual height of the tree. You must make sure your Cherry trees are either on Gisela 5 rootstock – which is dwarf and can be accommodate in 5-6’ of height – or use the old ‘festooning’ technique which naturally restricts the height of the tree and encourages earlier fruiting.
All varieties would be suitable, including the less reliable older varieties which might represent an exciting possibility – but it remains the more modern self fertilising varieties that will bring the greatest rewards. Sunburst, Stella, Summer Sun, Regina and Lapins are all ideal, or the ‘white’ cherry Vega, which would be partnered by any of the forementioned.
Are a natural grown under cover and again, commercially they nearly always are nowadays. For the home gardener the benefits include not only bird protection and clean fruits that haven’t been softened or marked by rain or hail, but also a greatly extended season. I would recommend growing any combination of Emily, Cambridge Vigour, Elvira or Gorella which have natural earliness that that will be greatly enhanced by a protected environment. You will be harvesting ripe strawberries by early May most seasons. And, at the other end of the season, make sure to include some Autumn fruiting/Perpetual varieties. These are varieties that crop from August right into the Autumn, usually they only stop ripening because of frost. In a Polythene tunnel they should continue yielding well beyond their normal season.
Might seem a strange choice for the Polythene tunnel but I know someone who regularly achieves crops of ‘Autumn Bliss’ until December by growing them in just such an environment, The principal is the same as with the Autumn fruiting strawberries discussed previously. Autumn Bliss is also naturally compact so it won’t outgrow the available head space. I probably wouldn’t bother growing other Raspberries with protection, although you could maybe consider an early variety such as Malling Promise which could bring you extra-early ripe berries. When growing Raspberries under cover do watch out for rust which can be a problem.
If you can spare the space for a clump of early Rhubarb in one corner then it will be ‘forced’ into providing extra juicy and sweet early Spears. Timperley Early is an ideal choice that will give you pullable sticks in February with no added attention whatsoever; that’s got to be worth having!
Grape Vines
Are a natural choice for cultivation in a Polythene tunnel and all varieties are very suitable. Dessert grapes develop new levels of sweetness and the bunches may be larger and more well filled. Unless your tunnel is large you will need to cultivate using a restrictive growing system such as multi-cordon but Grapes thrive on hard pruning and are generally easy to keep within bounds.
Peaches, Apricots & Nectarines
All can be grown outdoors in favoured spots or warmer locales. But when you grow them under glass or polythene the results are vastly superior. The naturally early blossom is protected from late frosts and sets reliable yields. The added summer warmth gives big, luscious, properly ripe fruits that will be the envy of your neighbours! Grow these as small bushes; Peaches and Nectarines are quite easily contained but Apricots are more vigorous. Stick to the naturally compact ‘Isabelle’.
Will do well under cover as long as provided with an acid/ericaceous growing medium and make sure they do not dry out at the roots. The berries will be protected more from birds which love Blueberries!
Further notes on growing fruit under cover.
Irrigiation will be necessary regularly, even if you are growing direct in the ground. The soil will get dry as the season advances so make sure you water every day with a hose. Try not to over-head spray, but water at the base. The problem with wet leaves on hot days under cover is that they can scorch as a result. And you don’t really want wet leaves and fruits in an already humid atmosphere because it will encourage disease. This is probably the most important aspect of growing in a polythene tunnel. It is an ideal breeding ground for moulds, fungus and mildew as well as red spider mite so be on guard and provide good ventilation wherever possible. This last point is also important to allow pollinating insects access to do their job. If there appears to be an absence of such insects hand pollination with a soft haired brush will increase the quantity and quality of yield for all fruits concerned.
I hope these notes will inspire the lucky Poly-tunnel owner, or maybe inspire you to invest in one for yourself. The boundaries of what you can achieve will be greatly extended. These tips can equally be applied to Glasshouse growing.

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