Strawberry 'planter' query

Last year, for the first time, I bought a 2' high strawberry 'planter' and 6 small plants. I had a few fruits but didn't expect too much although I made full use of the runners and now have a fairly respectable number of plants from which I can get yet more plants ad infinitum.

I was always told (whether it's true or not I'm not sure), that strawberries are a '5 year plant' - 1 year to grow, 3 to bear good fruit but with a falling off in the 5th year.

My 6 original plants survived the winter and now have lots of fruit but I'm wondering how long they can remain in the same pot, with the same soil. I water them (a lot - especially this weather) and give them an occasional dilute tomato feed but isn't 5 years in what seems a small amount of compost for 6 quite large plants, a long time? And what, if anything, should I do about it?

 

I re-pot mine in fresh compost each spring.

 

Its a moot point here, blackbird keeps eating them :(

 

The other half and our daughter keep eating mine!

I've got mine in a lined shopping trolley. I pack straw around the growing plants just before flowering and I find this and the annual leaf fall rotting down helps replenish lost nutrients in the soil and the occasional top up with tomato feed is all that's required. My plants are 4 years old and I've had a massive crop this year, I also use different variaties to prolong the cropping season.