Harvest time! Delights and diseases.

A box full of potatoes
My tattie harvest tucked away nicely for later:)

It’s been a while since I picked my tatties at the beginning of October but I have been waiting for my courgette plant to stop cropping before I reflected on the magnitude of my overall bag-garden harvest. I picked my last miserable looking yet very flavoursome courgette about a week ago, so it is now time.

I have to say that the tattie picking has made me feel a bit schizophrenic. On the one hand, I felt a little bit glamorous, like Matt Damon’s character from The Martian – an astronautical botanist, setting up a successful potato farm on the inhospitable Mars to feed himself after he gets stranded there alone for years. His MacGyverish survival skills are certainly something to aspire to;)

Or was I more akin to the Scottish school children of the post-war decades, recruited for their annual ‘tattie howking’ over the October potato picking holiday?  Basically, feeling a bit exploited but glad of the chance to muck about outside and the pocket money… On her Alba Living blog, Jean eloquently reflects on the potato’s history, including tattie howking – the legitimised kiddie hard labour making for a puzzling and even disturbing part of the picture to both of us, newcomers in Scotland. The official recruitment videos are a blast though! See here and here. The goverment-sponsored recruitment was pretty much gone by the 1960s, and the October school holiday is the only remaining memento. I am sure my bag harvest was much less labour intensive than digging the blighters out of the ground, but it was still quite a messy, protracted and rather unglamorous affair…

Grow bag with compost emptied out
Harvesting the potatoes was a bit of a effort!

So how did I do? I think not bad at almost 10.5 kg of potatoes from the 5 bags! I haven’t had to buy any since the harvest over a moth ago, and there are still plenty left, securely tucked away in the darkness of a large storage box on the balcony. This yield was produced from 4 varieties with 4-5 seed potatoes each – or 16-20 seed potatoes. Unfortunately, I cannot calculate the exact seed-to-crop weight ratio as I did not weigh the seeds before planting. But based on Bridgend Nursery’s data we can assume that, on average, a seed potato was around 78g , which gives us a return rate of 6.7 – 8.4x.

Tubers of the 4 potato varieties
My lovelies (from left to right): Apache, Highland Burgundy Red, Isle of Jura, Arran Victory

This is below the average expected from ground-grown maincrops which is around 13x, as given by Dr Hessayon in The Vegetable Expert and George Seddon in Your Kitchen Garden. Which is not surprising, given that I put in my potatoes very late, at the end of May, and had to pull out them early due to the late blight attack. This gave my plants only 18 weeks for growth instead of the recommended 22 weeks. From reading around, it also seems that yield in container-grown potatoes is significantly lower to those grown in the ground, perhaps because the roots tend to dry out more easily and get uncomfortably warm (tatties do like their footsies nice and cool). See a useful summary on growveg.com. Variety can also make a big difference – as it seemed to be the case with my crop as shown on the graph below.

A graph of yields for the 4 potato varieties
Great yields!

Apache seemed like the poorest performer by weight but it started off as much more ‘overchitted’ seeds compared to the others. I think this caused 3 out of 5 plants to die early after being earthed up. However, its tubers were the largest and the least affected by disease. It was also very delicious and made brilliant wedges (our favourite potato dish of all time). I will definitely try it again.

Isle of Jura and Arran Victory were mid-range performers by weight, with Arran Vic winning on the interest front with its funky purple skin. Both are nice tasting as wedges and mash.

Highland Burgundy Red stunned me with a yield of nearly 4 kg! Perhaps splitting the seed tubers between two bags gave it more space to grow? It is also by far the most interesting colour-wise and its flesh does retain its glorious pink when boiled gently for mash or grated and fried in placki ziemniaczane (Polish potato cakes). I am saving some of it to make pink kopytka (Polish gnocchi). Perhaps I will have some time to blog about some delish Polish potato recipes later on…

Next year, I may try some of the varieties that RHS recommends as highest yielding for bag growing based on their 2013 experiment (PDF).

Courgettes on the scales
The weighing of the courgettes

What about the courgette, you ask? I got almost 1.5 kg of the lovely things over the growing season. I must say that it was far from an overwhelming crop, especially for courgette addicts like us, so next year I will try for two plants and an earlier planting out date.

So overall I had almost 12kg of food coming out of the bag garden, which covers an area of around 2.25 m². That makes for around 5.3 kg/m²! UK urban gardens and allotments produce 3.1-4 kg/m2 annually although the yields can apparently be as high as 8.83 kg/m². Most importantly, our project funders, CCF, assume productivity of 3 kg/m² annually for their food-based carbon footprint reduction projects, based on National Society of Allotments and Leisure Gardeners figures (PDF). By these standards I think I shall do quite well in our Tayport Carbon Challenge next year! But –  once I include more of the salady crops, the overall weight will inevitably go down…hmmm.

Of course, my ultimate dream is to get to grow as much as Vertical Veg’s Mark Ridsdill Smith on his balcony and windowsills in London – 84 kg of food worth £900 in his 2010 season. If only!

That’s all for the productivity. But I must touch on a darker topic – the diseases!

Leaves with brown patches on them
First symptoms of late potato blight

I was quite smug about my tatties’ rude health, while Margaret and Cathy had to take theirs out mid-summer, until late blight (Phytophthora infestans) hit them at the end of August. And what a terrifyingly swift hit it was! It took only one weekend away for all the plants to develop soggy brown splodges on their leaves. Thankfully, the AHDB’s advice suggesting immediately chopping off the haulms to stop the disease from progressing into the soil seems to have worked. I was extra paranoid and also washed the potatoes thoroughly before letting them dry off, which substantially contributed to the pain at harvest time… It looks like there is no sure-fire way of avoiding blight really, although earlies and resistant varieties are less likely to get affected. So I will stay vigilant, and maybe even keep an eye on smith period alerts via Fight Against Blight service

But I was not even prepared for what was happening underground. Frustratingly, the scabby surface of the tubers was only revealed at harvest time:( According to RHS, there were two possibilities – common scab or powdery scab (just to be safe, I also cross checked with the AHDB potato disease database). Even more frustratingly, one is more likely when the soil is kept too dry, the other – when conditions are too wet. So it is important to work out the scab’s true nature in order to avoid reoccurrence in the future. Luckily, the damage is largely cosmetic and peeling the skin gets rid of the unsightliness…

It is a bit of a stab in the dark, but I think it may be the common scab. It’s been a wet summer, and I wasn’t watering the plants for fear of making them too wet. With bags heating up, and tubers packed in tightly it is likely that they were not getting enough water at the critical tuber-formation period. The compost’s pH might have been too high too – I did use some manure to enrich it after all…

Do you think that I am right?

If so, I’d better avoid using the soil for the alternate hosts next year – radishes, beetroot,  swedes and turnips…

The biology of the scab-causing critters really piqued my interest, they are nothing as straight forward as the fungal blight according to the RHS:

Both the common and powdery scab pathogens are sometimes described as fungi, but in fact Streptomyces scabies is more closely related to bacteria and Spongospora subterranea f. sp. subterranea is related to the slime moulds.

But perhaps this is a story for another time!

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