Well, with anything you might have to do a little weeding, but Geranium 'Biokovo' or 'Karmina' are quite weed proof once established. Deer proof too.

Have to ask though, don't you want shade on a deck that "gets blasted by the full sun"?

Yes, weeds will still come in until the ground cover is thickly established and even then you will still need to keep an eye out for seedlings.

if you want help it might behoove you to post a few pix of the situation ...

what is your base soil type..

ken

never put down landscape fabric..

but that said.. you prevent or deter weeds with a nice thick mulch...

ANY BARE EARTH.. will sprout weed seed ... most is air borne.. and what isnt.. is also air born via birds ...

day lily can clump up rather nicely.. over a few years.. and in the mean time.... the mulch will do the job..

ken

Thanks everyone. I’ll definitely look into those geraniums. We have a large umbrella for us on the deck lol.

We haven’t mulched the entire area yet (3rd trimester pregnant with a 16 month old at home, trying to juggle it all)! The base soil is heavy clay. Like if it gets wet, it’s like you’re at a pottery making class. I did try small evergreens there once, and they didn’t survive the winter burn from the wind they get.

I doubt any groundcover will completely deter weed growth. I have a 2 and 1/2 foot thick layer of evergreen English ivy covering the ground in the adjoining greenbelt and weeds grow right through it. If weeds can grow through ivy, they can grow through anything!!

True, nothing will completly prevent weeds, but those geraniums are extrememly weed suppressing.

Geranium Biokovo could struggle with the heavy clay soil, I have a loam with some clay in it, with full sun and dry-ish summers & wet winters.

Geranium x magnificum Rosemoor does well, it takes about 2 year to get started, after that it is quite competitive.

another one on the thuggisch side ist Geranium endressii which tends to selfseed but is almost undestructible

both grow about a bit under 2 feet tall

mulching after planting will help to reduce the weeding immedialtely after

and I think that English is superb in part shade but not in full sun regarding the competitiveness

Try growing a dwarf form of Comfrey - there is a fairly true blue flowered variety that I can't think of the name of right now - at any rate, comfrey will grow in the full hot blazing sun and nothing will grow under it because it grows very full and thickly, sort of like a hosta for full sun.

Here it is, Hidcote blue -

https://www.highcountrygardens.com/perennial-plants/unique-plants/symphytum-hidcote-blue-comfrey

I have both 'Biokovo' and 'Karmina' as well as G. maccrorrhizum in very heavy clay and all are doing great. In full bloom now.

Thuja occidentalis 'Mossy' works for me.