Sweet Potatoes

I brought some sweet potato slips and put them in a pot for 3 seeks then transplanted to builders bag full of compost and manure, 16 weeks later I decided to have a look and all I got was very thin worm shaped and length potato, I had 5 slips in the bag, the flowers were out and leaves/foliage was massive, don't understand why they didn't grow?
even if they were to close or didn't water enough still expected better growth than that

 

you will probably be better posting this in the 'edible gardening' section.

There's some good vegetable growing knowledge in there

Did you grow these outside or in a polytunnel/greenhouse?

I believe sweet potatoes need a lot of warmth

 

Having tried to grow them once, I'm convinced our growing season is mostly too cold and not long enough.
Must admit I was only experimenting using supermarket bought, not those plants sold as ideal for the uk climate.
But I ended up with lots of top growth and no tubers, I think the plant probably forms the tubers as the tops are dying down naturally, not something they are likely to do in this part of the world.

 

So might be best planting them really early and protecting against frost so that they have a good long season?

 

Same as me lots off top growth not much else, I got the UK one's and nothing. Thanks all for your advice

 

I planted them when the supplier advised to plant them, Marshall's only sent them when they think it's ready to plant which was in May

 

Perhaps some bottom heat (a warming cable) might help