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Green, Vegetable Garden

Will You Ditch the Chemicals and Choose Blight Resistant Potatoes This Year?

February 8, 2013

As a result of conversations with community gardeners this week, today’s post looks at the alternative to spraying for potato blight every year, by planting blight resistant varieties instead.

I’ve written an extensive post on choosing, understanding the terminology and growing potatoes in the past. I’ve also written one listing eight ways of managing potato blight, but as minds turn towards garden centre shelves and catalogues full of seed potatoes, blight resistant varieties can offer a real alternative to spraying.

Why Choose Blight Resistant Potatoes?

potato blight

potato blight

If you choose blight resistant varieties it will eliminate the need to spray with fungicides. I remember Irish weather forecaster Evelyn Cussack telling us that Ireland sees blight conditions nine years out of ten.

For several years we’ve grown Sarpo Mira potatoes in our garden. They’re a maincrop variety so are actively growing during the usual humid months that the blight fungus (Phytophthora infestans)  thrives. So far the Sarpos have never been infected with blight, even when the tomatoes succumbed (same vegetable families will pick up the same diseases).

Feeling complacent from our blight free years, last year I planted Red Duke of Yorks (not blight resistant but I’d heard they were delicious). I didn’t spray with the organic blight alternative Bordeaux Mixture, as we generally steer clear of all sprays here, organic or otherwise. It really didn’t come as a surprise when the day before we headed off to the US for the summer, I saw the first signs of blight appearing on leaves.

Chopping the plants off at soil level as soon as I spotted the initial signs (see picture above for symptoms) may well have saved my two potato beds from serious infection, but leaving the tubers in the soil for two months over a very wet summer while we were away didn’t. Despite the problems, we managed to save two small sackfuls and can rest assured that we now have vegetable beds full of very plump worms! I’ve learnt my lesson. From now on in I’ll be choosing one of the blight resistant varieties listed below. (If I’d planted Sarpos, because of their blight resistance they would have been growing throughout August, the foliage would have protected them from the worst of the wet weather and we wouldn’t have come home to mushy spuds.)

From a commercial point of view, farmers face great difficulties growing potatoes in Ireland with our unpredictable weather, as well as suffer huge expenses. Popular potatoes that we’re familiar with in greengrocers and supermarkets are likely to be sprayed 20+ times during their growing season (chemicals such as Dithane can be sprayed every 10-14 days). That’s a lot of unnecessary chemicals entering your bloodstream, however ‘safe’ they claim to be, when a home-grown chemical free alternative can be planted as an option.

anti gmo marchIn an attempt to address the problems faced by farmers, under a mass of controversy, Teagasc have been growing and researching genetically modified crops in a field in Carlow. Organic farmers and growers (myself included) have been up in arms about this development, concerned that humans are being used as guinea pigs for this untested science.

However, convincing commercial farmers to swap their tried, tested and popular potato varieties for blight free replacements will not be easy.

In 2012 SPUDS (Sustainable Potatoes United Development Project) run by the Lifeline Project in partnership with the Savari Research Trust asked Irish growers to grow naturally blight resistant potatoes (such as Sarpo Mira) as part of their research project (I missed the press release hence the Duke of Yorks). Their website is still under reconstruction so I can only assume they’re busy collating responses. I’m anticipating hearing good results given the feedback I’ve heard from other growers, as well as my own experiences of planting Sarpos.

blight resistant potatoesBlight Resistant Varieties available

For a full list of potato varieties and their resistance to various disease including early and late blight, see the The British Potato Variety Database which is regularly updated. The following includes the popular blight resistant varieties you should be able to find in your garden centres or online garden shops along with their waxy/floury qualities – one of the first question I’m asked by people looking for advice on what varieties to sow.

blight resistant potatoesIt’s important to note that the blight pathogen mutates regularly so potatoes that may once have been able to resist blight, may no longer be able to.

Have you grown blight resistant potatoes in the past? Did they resist the parasitic fungal disease and importantly if more people are to be encouraged to grow them, did you enjoy eating them? I’d love to hear your own experiences.

Green, Vegetable Garden

8 Tips for Managing Potato Blight

August 22, 2012

Potato BlightHere we are, almost at the end of August and three months after first being alerted, still hearing potato blight warnings in Ireland. Not surprising really given the damp warm conditions Ireland has been under for many weeks, but if you’re growing potatoes or tomatoes it’s imperative you keep vigilant.

Blight is tricky to control organically and there’s a lot of confusion about what home growers are ‘allowed’ to use or not.

A couple of years ago I was informed that I could use copper sulphate, which was available as Bluestone in most chemists and that I could make up my own Burgundy mixture (a mix of copper sulphate, washing soda & water).  However, on enquiry at the local pharmacy I was told that they were no longer allowed to sell Bluestone and that it was illegal to make up my own solution, so that scuppered that idea.

Potato BlightWhat can organic growers do to prevent blight affecting crops?

Blight is a parasitic fungus (Phytophthora infestans) that usually attacks in the summer months in humid conditions and is carried on the wind.  It can attack leaves, stems and tubers and can also cause Tomato Blight as tomatoes and potatoes are in the same (Solanacea) family.

  1. The method that has been the most effective in my experience is to plant resistant varieties. Sarpo Miras (an early maincrop), Sarpa Axona (maincrop) and Blue Danube (early maincrop) all show excellent blight resistance. Setanta (maincrop) and Orla (early) are Irish varieties that have shown good resistance too.
  2. Planting early crops of potatoes (new potatoes) will help as the idea is that they will have matured before blight warnings are issued. However, in 2011 warnings were issued mid-May so that can’t always be guaranteed.
  3. Keep earthing up potatoes as they grow (bringing the soil up around the stems). This will help to protect the potato tubers in the ground should blight attack.
  4. When placing the seed potatoes into the soil, use the maximum spacing suggested. This will ensure there’s an airflow between growing plants.
  5. Practice good crop rotation
  6. Good hygiene. Ensure beds are as weed free as possible.
  7. Vigilance. If you notice blight on the leaves, cut the stems at ground level leaving the tubers in the ground for at least ten days before moving them. Unless you have a really hot compost system, you will need to move the foliage away from your site, disposing of it safely. Blight is often recognised by a white furry ring on the underside of leaves that outlines the brown splodge (see top picture).
  8. If none of those methods appeal or you’ve tried them before and they haven’t

    image courtesy The Secret Garden Centre

    worked, Bordeaux Mixture is approved for organic use and can be sprayed onto your crops. (Thanks to @KathyMarsh for the update: Under Irish organic standards you may use up to 6kg per hectare per year. You no longer have to ask permission but must record why you used it.) This is a preventative measure however and should be sprayed before the risk of blight. It’ll be no good whatsoever spraying it on afterwards. Bordeaux Mixture is available from good garden centres or online.

It’s difficult to talk about blight without mentioning the GM potato trials that will going on in Teagasc at Oak Park, Carlow that many of us alarmed by the increase in GM crops are nervous about. I’ve written about GM in previous posts and here’s a link to an excellent article in explaining that GM crops aren’t just about the science – they’re about the politics. are running an awareness campaign to educate the public about the availability of naturally blight resistant varieties that are available in Ireland. If you’d like to find out more about what they’re doing, please head over to their website, sign up for their newsletter and show them some support.

Have your crops been affected by blight this year? Did you find that planting resistant varieties has helped?

Vegetable Garden

Potatoes – All you need to know to help you grow your own

February 19, 2010

(This photo shows the variety Sarpo Mira, a blight resistant late maincrop, interplanted with the companion plant Borage.)

I love growing potatoes as each time I harvest them I feel like I’m unearthing buried treasure (making it a real joy when our children help)! Carefully loosening the earth from around the plants and seeing how many tubers have grown from one little seed potato carefully planted weeks before is a real delight. However, the range and variety of potatoes available, as well as all the gardening terms used when talking about them, can seem quite bewildering to someone new to growing veg.

As a result of all the questions I’ve been asked recently about this magical crop, including  “what are earlies”, “how should I plant them?” “What’s blight” “what are floury/waxy potatoes” “what do you recommend”, the following is a guide to choosing and growing your own spuds.

Potato Groups

Potatoes are put into groups that describe how long it takes for them to reach maturity. Usually this is about:

Very early earlies        – 75 days (harvest around June)
Earlies (or 1st earlies)  – 90 days (harvest around July)
Second Earlies            – 110 days (harvest around August)
Early Maincrop            – 135 days (harvest around September)

Late Maincrop             – 160 days (harvest around October)

Earlies are often described as ‘new’ potatoes as they’re used when fresh rather than stored. They’re also planted closer together so are smaller and take up less space. They’re a great crop to grow if you’re nervous about growing spuds for the first time. Apart from harvesting them at a time when new potatoes are expensive in the shops, because they’re ready early to mid summer they usually avoid pests and diseases such as blight and potato cyst eelworm.

Maincrops are great for storage but can be used straight from the ground too. Every year more varieties of blight resistant varieties are introduced in an effort to combat this destructive fungus.


Potatoes are grown from what’s known as ‘seed potatoes’ readily available from garden centres, DIY stores and mail order catalogues from mid winter onwards. It’s not advised to save your own (or use supermarket potatoes usually destined for the table) as they may become diseased. If you have a choice when choosing potatoes, try and pick larger tubers for early crops and small/medium sized for maincrops.

There’s a lot of debate about lately on whether we should ‘chit’ potatoes prior to planting. Chitting means that you’re encouraging the potato to sprout before placing it in the ground in the hope of an earlier harvest. Potato tubers will eventually form on these sprouts.

Often gardeners will chit earlies but plant maincrops as they are. Chitting involves placing the seed potato (known as a tuber) in a container (like an egg box) and placing it in a dry, frost free room out of direct light so that it grows little shoots out of it’s ‘eyes’.

When the shoots are approximately 2.5cm long the potatoes can be sown outside. Don’t worry if they’re longer – just be careful not to snap the shoots off.

When can you plant them out? The soil where the tuber will rest should have reached a temperature of about 6oC for three consecutive days (usually March to April). Don’t attempt to plant them if the soil is too wet, sticky, dry or frozen. If you’re worried that the conditions don’t seem ideal and time is passing, try pegging down some clear plastic over your soil to help warm it up. The yields will be much higher in a long growing season.

Growing Methods

In general, the closer you plant the seed potatoes together, the smaller the harvested crop. As a general guide when sowing in rows, place

Earlies – 30cm apart, with 60cm between rows and 5cm deep

Maincrops – 37cm apart, with 75cm between rows and 10cm deep

They will grow in most soil types but prefer a sunny, frost-free area with a pH of 4.5 to 6. Potatoes can be a useful crop for breaking up soil as their roots are so deep. If you can, manure the soil the previous autumn as this crop is a greedy one. Once the plants are growing they will need watering – heavily and every week on dry soils.

Potato crops are not fully hardy. This means a heavy frost could kill them (as farmers have found to their cost this year in Ireland) and we have been known to have snow as late as May. If you can, cover the growing crops with horticultural fleece, newspaper or cloches to protect them if frost threatens.

Container planting choose a compact variety – early and second earlies are ideal. Plant 3 – 4 seed potatoes in compost in a large container (such as a dustbin or a heavy-duty plastic sack with drainage holes punched in the base) at a depth of about 15cm. When the foliage starts to grow (known as the haulm) add more compost to “earth up”. This encourages more side shoots to develop. Keep adding compost until it reaches the top of the container.

Planting in the soil there are a couple of popular methods used for planting outside. The first involves making V shaped ridges in the soil and planting the tubers in the bottom, using the soil on the ridge to ‘earth up’ the foliage (haulm) as it grows. The second method involves covering the soil with black plastic or weed membrane, making little X shaped cuts and planting the potatoes directly into the soil, making the slit larger as the plant grows.

The reason for earthing up or covering the soil with plastic is twofold. Firstly it prevents ‘greening’. As the plant grows the newly developing tubers get pushed upwards. If they’re exposed to sunlight they become green and produce a poisonous toxin called solanine. Secondly earthing up will give the tubers some protection against blight. If you choose to earth them up, do so in the morning – potatoes tend to droop as the day progresses making the job harder.


There are over 100 potato diseases, which is enough to put anybody off growing them! In my experience the main ones to worry about are Blight and Eelworm – not to dismiss all the others but these are the nasties. Slugs also love potato plants so a daily patrol at dusk armed with a torch and an empty milk container half filled with salty hot water will keep them at bay.

Blight is at its worst in warm, humid conditions usually from July onwards. It’s a parasitic fungus that’s carried along in the wind currents. Beginners often find it a difficult disease to diagnose until it’s too late. Look out for brownish-black spots that appear on the leaves and stems. The undersides of leaves often have a white mould fringe around the spots. Tubers will have black marks on them.

Once it’s taken hold there’s nothing you can do other than remove the haulms (do not compost them) to about 5cm off the soil level and hope that the spores did not infect the tubers in the soil. Affected tubers cannot be stored. If they are infected the black marks can be cut out and the rest of the potato eaten but avoid giving them to pregnant women, the elderly or sick.

Avoid blight by buying resistant varieties, planting earlies and earthing up. Also dig up all tubers when harvesting and remove any infected plants from your site.

There are eight tips here for managing potato blight without chemicals.

Potato Cyst Eelworm This pest is very common in soil that has had potatoes grown on it previously. The plants are often stunted, with leaves that turn yellow and die. If you suspect eelworm Joy Larkcom in her great book Grow Your Own Vegetables suggests lifting the roots and plunging them in a bucket of water – the cysts will float on the surface. You may have to give up growing potatoes in that area for 10 years if infected!

To prevent Eelworm infestation follow a long crop rotation, grow resistant varieties, and only grow earlies (they mature before a major infection occurs) and only use certified seed.

Incidentally, Scab is caused by growing potatoes in soil that is too alkaline (high pH of 7 or more (they’re still safe to eat though).


You can start harvesting most varieties once they start to flower. With earlies just dig them up when you want them – preferably just before dinner! Maincrops too can be dug up as required but if you want to store them, and they’re healthy, they can be left in the ground until early autumn.

If you notice that your plants are starting to look diseased, don’t delay – cut back the haulms to ground level and leave the tubers in the ground for about two weeks before lifting which will help their skins to harden.

Varieties and Quantities

How do you decide what seed potatoes to buy and how many? There are over 500 varieties on offer all with different traits. Whether you grow waxy or floury potatoes is personal preference – what do you like to eat and cook?

Waxy potatoes are translucent and feel moist. They’re firmer and keep their shape, making them ideal for salads, chipping and boiling. Varieties include Coleen, Charlotte, Marie Peer, Aaron and Remarka.

Floury potatoes are drier and granular and are best where you want fluffy potatoes for roasting or mashing. Varieties include Estima, Records, Setanta, Maris Piper, Desiree, Golden Wonder and British Queens.

Other points to bear in mind include what variety best suits your area/location? For instance Epicure are a floury potato with more frost resistance than other varieties, making them an ideal choice for colder areas. The Sarpo range has been bred for their blight tolerance. Charlottes are a classic salad potato with good blight and scab resistance and Maris Piper have a good resistance to eelworm.

If you prefer to purchase your potatoes from the local garden centre, take a look through your gardening books or seed catalogues and jot down a few choices before you leave home. If your main consideration is culinary, check out which has a comprehensive list of varieties and their best uses.

As a general guide to how many to buy and plant, potatoes are usually sold by weight. 1.5kg gives an average of 14 seed potatoes and requires and area of roughly 2.5sq metres to grow. The total yield will be an average of 10.5kg (depending upon variety and growing conditions).


If your crop is healthy it’s much more likely to withstand attacks from disease and bad weather. A seaweed based foliar spray can be applied at least three times during your plant’s lifetime (including while they’re chitting) to give them a boost.

Copper sprays can be used against blight (the Irish organic standards for using copper based sprays are 8kg copper per hectare per season). Contact organic suppliers for more information.

If you can contain horseradish by planting it in a bucket at the end of the row (it can get invasive), it’s said to provide general protection to potato crops. Evidence is also showing that substances from the roots of Tagete patula (marigolds) can help to prevent microscopic eelworms and Borage is said to repel them.

So that’s it. Have a go! Good luck.