Underplanting Pyracantha & other large shrubs:

Elothir

We have a very large  Pyracantha that unfortunately has a fairly noticeable patch  of mostly bare soil underneath it with the exception of a well established Sedum spectabile (or at least something like it). Because of the shape of the Pyracantha, about half the area under it gets a good amount of sunlight in the morning through to early afternoon depending (obviously the other half is more or less shade all day), but the soil is rather heavy clay.

It would be nice to get some more plants in to fill in the bare soil, but I don't want to do anything that could harm (even slightly) the Pyracantha (or the sedum for that matter). 

So I was wondering if anyone had any advice, both for plants that might work, and for avoiding harm to the Pyracantha/it's roots etc. I was leaning towards finding some seeds to sow rather than young plants to plant as I would think the less digging the better. 

Of course it's entirely possible I'm being overly cautious given its a large, old Pyracantha.

KeenOnGreen

You are probably being over cautious.  I would be more worried about the Pyracantha taking up all the water and nutrients and anything under it being compromised.  We have a 30 year old Pyracantha hedge which has similar conditions to yours.  We underplanted with bulbs (species tulips, crocus, hyacinth).  They are all doing reasonably well, but we mulch under the hedge each year to retain moisture and add nutrients. 

Fairygirl

I have loads of planting in front of pyracanthas. Mine form part of a loose hedge with buddleias and viburnum, and there's laurel and white spirea nearby. In front I have bulbs, dicentra, astilbe, ferns, heucheras, geraniums and hostas. They were all planted after the pyracnatha was quite well established. 
It's basically east facing, and doesn't get huge amounts of sun, but we do have a fair amount of regular rain, and we're on clay, albeit well improved. It never dries out in that section. 

Loxley

Go with Margery Fish's advice - if in doubt, plant a geranium. Geranium 'Anne Thompson' is a good one that flowers June-Oct (you could underplant with Pulmonaria or bulbs for spring interest) or you could go with a mass planting of Geranium macrorrhizum which doesn't flower for as long or as intensely, but has nice neat semi-evergreen foliage.

A little digging won't hurt the Pyracantha too much, you could plant 9cm plants and mulch really well rather than cultivating the ground, to avoid serious digging.