Do I need to cut them back ?
It looks like it will have a few blooms again. You can cut back foliage that has withered from its earlier bloom. I would let any stragglers bloom before cutting them back. Do you overwinter inside or leave them outside? Since yours are in a pot, I'm thinking you move them to a sheltered location or to a garage.
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19371
https://www.gardeningknowhow.com/ornamental/bulbs/agapanthus/agapanthus-flowering.htm
In West Sussex clay type soil
This article should help:
https://www.gardeningknowhow.com/ornamental/bulbs/agapanthus/agapanthus-not-flowering.htm
How do I get rid of the grass without killing the plant?
There are products that can kill grass among ornamentals but you have to make sure your plant is on their list of safe plants. Since agapanthus has grassy type leaves, it may not be on the list.
Failing that, you can dig out the grass, trying very hard to get all the pieces of it.
If the agapanthus is not too widespread, you can dig up the bulbs, spray the grass with a non-selective herbicide, then replant.
https://www.gardeningknowhow.com/plant-problems/weeds/grass-growing-in-flower-bed.htm
Variety Queen Mother. Wasnt able to divide for last two years. very large strong growth six to eight inches above the pot rim showing many green roots on surface and up rhizomes. Managed to remove from pot and divided but not sure how much need leaving above new soil surface. None of my pots are deeper then 14 inches and from old base roots to where new green shoots are is over 24 inches. Can bottom half of root ball be cut away?
You can knock out some of the soil and trim away dead roots. If the roots are very long, it shouldn't hurt to clip them back some. That should reduce the size of your root ball so you can replant.
https://www.gardeningknowhow.com/ornamental/bulbs/agapanthus/dividing-agapanthus-plants.htm
https://www.gardeningknowhow.com/ornamental/bulbs/agapanthus/dividing-agapanthus-plants.htm
Will it need breaking up
We have just the article to cover these subjects!
https://www.gardeningknowhow.com/ornamental/bulbs/agapanthus/dividing-agapanthus-plants.htm
e & well but I\'ve had it for two summer seasons now & have yet to have any flowers! Any advice?
Usually, a lack of flowers will indicate a lack of phosphorus and potassium, or too much nitrogen present in the soil. There are a few other factors that could be the issue, but testing for soil nutrient imbalances will be the first thing that I would recommend.
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
This collection of articles will help you with the care of Agapanthus:
https://www.gardeningknowhow.com/ornamental/bulbs/agapanthus
I live in zone 8 and it is in full sun.
Because all of the other factors are likely within range, I suspect that there may be too much nitrogen and not enough phosphorus and potassium in the soil. Fertilizers for BLOOMING plants will help, should a test reveal a lack of phosphorus and potassium.
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/ornamental/bulbs/agapanthus/agapanthus-not-flowering.htm
https://www.gardeningknowhow.com/ornamental/bulbs/agapanthus