As well as the allotment, I decided to get one of Marshalls set of 3 Growing sacs, plus spuds (Mozart, Accent and Charlotte). I started these indoors in February, and had to put them out by March because they were growing so fast.

I protected them from frost, continued to earth up and the foliage looked really lush & voluminous. Through some of the hot spells in Mar/April I may not have kept pace with watering, though I did catch up. Over the last 4 weeks the foliage has died down, or shown brown patches. This has also happened with my Charlottes in the allotment.

When I went to have a look in the bags last week, i was very dissapointed. For the Mozart and Accent, there were about enough potatoes for 2-3 portions in each bag! Most were very small, one or two were up to 3" long. Taste was average. I wouldn't have minded if the plants hadn't grown well but the foliage was around 2' above the top of the bags.

Was I just unlucky?

I would guess that the initial problem was with watering. If you don't get that right, in particular at the stage when they are forming tubers then they get aborted so few form.

I grew 10 tubers of Premiere in 13 litres plastic bags, starting them off in the greenhouse until needed for the toms. Needed constant watering during the hot weather, sometimes twice a day or more. Not a great yield, perhaps 9-10 tubers per plant, but great flavour. Will certainly grow more next year.

Hi Colin_ M,
Do you think that the choice of growing medium had anything to do with the final outcome?
JB,

It's possible.
I used the same JI multipurpose compost that I use to pot on all seedlings and which usually works well. In addition, Marshalls provided a small quantity of Potato fertilizer which I added at the recommended stage.

I'm certain that the growing medium plays a large part in final yield (as well as watering). I grow all my spuds in containers and use a mix which contains about one third soil and also lots of organic matter augmented with BFB and a liquid feed. If you just use a commercial compost you are not going to have enough nutrients in the mix to sustain the growing crop.

I have also posted this partly under 'taste - compost'. Apologies, but think it quite important. Maybe move or edit some of it?

I had a problem with Charlotte yield a couple of years ago and this is what Alan Romans told me..

'Your situation is probably down to the watering at two key growing stages. You may have noticed that growers are always keen to organize irrigation for surprisingly young plants in the late Spring. This is because when the plant “decides” on how many tubers to set at the “hook” stage soil must be moist if lots are to set. There is then another key stage a week or two later when the plant “decides” how many tubers to fill out – again moist soil determines outcome. Pots dry out very quickly and even with care it is easy to stress the young plants without noticing – they won’t even wilt slightly because they are getting emergency rations from the mother tuber. You describe the signs of water stress at the first key stage perfectly. Water little and often and enjoy the fewer but much larger Charlotte you will get. '

Thanks Colin Miles, I have always had "adequate" results in the allotment and only rarely watered. Certainly I'm not scientific to know at what stage in the growing cycle the two points you mention occur.

Guess anything in a container needs closer attention than plants in the ground.

Hi other Colin. Not me who is the expert but Alan Romans. But it all points to the difficulties with watering in pots, especially if the compost is one that isn't as wettable or moisture-retentive as it should be. Even with 'ordinary' garden soil with my 13 litre plastic bags I have often been surprised at how dry the soil is, despite being careful, or trying to be. Although I grow my tomatoes in growpot on top of growbags I am still very uncertain as to how wet the compost is other than on the surface.

Is there a device out there which will tell you the wetness of pots?

We always do a series of potatoes in tubs in the tunnels (13 this year) with the aim of having early crops. They take a lot of water and feed but they're always first class in terms of yield and taste.

We only put 3 tubers into each barrel and we top up the soil - a mixture of manure, chicken pellets and compost - as the green shoots appear. Then we stop adding anything except water and feed.

Maybe we've just been lucky! This year we've used 4 differet varieties.

Hi Tigger - I had 10 pots of Premiere which I started off in the greenhouse and kept there until I needed the room for the tomatoes. A good tasty crop - not great in yield but adequate. Like you did just cover them to start with then added soil until top of pot reached. Did need a lot of careful watering.

And at this time of the year - when we've run out of room to top up the soil - lots of regular feeds.

So out of interest, if these were growing in an open field, you wouldn't be adding feed at the same rate? Just relying on sufficient natural or added levels in the soil? I assume the more limited room for roots to reach out in patio bags is the reason for needing to add so much extra feed?

The ones grown outside sit on a substantial layer of manure with a hefty sprinkling of chicken pellets. The tubs have some manure in the bottom and some pellets but we always add a liquid feed each week.

it's not scientific but it works!