There used to be a form (clone?) around that grew more like an ivy or bearberry - more in one direction - and wasn't so fruitful that seems to have become largely replaced at outlets by the UBC introduction. The latter grows evenly in all directions and is often studded with fruits. Search Rubus pentalobus 'Formosan Carpet'.

Different varietals could be an explanation, but I see plantings ten feet apart on properties that were likely the same variety and one is fruit-loaded and the other has few or none. And some plantings have many fruits one year and none the next. A no-sprinkler-system landscape strip on Barbur Boulevard has plants that do this.

Too bad, because I find these berries tastier that salmonberries, for one similar example.

Thanks, I really like this ground cover except that it doesn't shut out grasses and some other weeds. It is very tough and spreads well. I may pursue getting a variety that fruits better. Or would it need a lot more water to do as well, and fruit?

I doubt that water is the trick for getting this plant to fruit as the bloom and fruit set occur during the latter stages of our wet period. It could be that some water is needed for the fruit to fill out and reach normal size in July and August, during hot summers.

I really like this ground cover except that it doesn't shut out grasses and some other weeds

One of the primary reasons I like this GC better than most others is because IME it more effectively suppresses and smothers weeds and weed grasses than just about any other groundcover you could encounter. I've used it in numerous instances when other types of GC's have failed to deal well with with competing weeds and the rubus always wins out hands down. Perhaps it just need a bit more time to establish for it to demonstrate that quality properly to the OP, as its layering quality and evergreen nature are a virtually guaranteed weed block! Add to that its well behaved nature, relatively rapid establishment, adaptability to a wide range of sites and tasty fruit, what's not to like??

Easily my favorite GC for a wide variety of applications.

The Rubus 'Emerald Carpet' is around 15 years old, but had some large Mugho pines planted in it by a driveway. We removed the pines so there was some thinner growth where they had been, and a small amount of grass had been hard to remove along with thistles under the pine. Then we were traveling most of June last year and they went to seed, so lots of grass came up this year. Hopefully it will thicken up there enough to shut it out.

But I can tell you my most successful gc's for shutting out grass, first is gc comfrey, Symphytum grandiflorum, which gets close to no weeds. Then Geranium oxonianum 'Claridge Druce' has been very good, getting 2-3' tall and blooming for several months. Geranium macrorrhizum has been excellent in dry shade. Not to mention Vinca major. That is because although it shuts everything out with 2-3' deep vines, it is very rampant and therefore hated, and the little native blackberries do sometimes manage to invade it. But the areas under our Red Cedars used to be weed problems before these ground covers were planted.

Here is a link that might be useful: geraniums that spread

Hand weeding the rubus can be murder as it is armed with prickles. And extracting weeds can pull up part of the groundcover mat, which then has to be pushed back.

This plant is great for smothering weeds here. I've never noticed fruit on mine. It looks like it begins to form and then drops off, presumably because I don't water it at all. Here is an early morning photo:

That last picture looks more like Rubus tricolor. Forestfarm sent me 'Betty Ashburner' one time, it had a shorter leaf - maybe you have that one. I can't compare with mine because it did not take hold and persist. But there are pictures online.

There are also online indications that the more common one is supposed to be called by the 1984 name Rubus hayata-koidzumii instead of R. calycinoides, pentalobus etc. Awhile back UBC was calling their introduction 'Formosan Carpet' instead of 'Emerald Carpet'. I'd suspect a more abundantly fruiting planting of consisting of this clone.

Bboy, the rubus was given to me years ago and I was told that it was R. calycinoides, but I think you might be right about it possibly being R. tricolor (or at least having some tricolor in it). I can't really tell for sure just by looking at pics online, but at the Forest Farm site I noticed that R. tricolor is also referred to as "mounding Himalayan groundcover" and I think that describes the habit of my plant better than "creeping". Regardless of the name, it works well as an attractive and low maintenance groundcover here.

I saw these plants last year when looking for a big Loquat in the area.They are in a flower bed that spans just about the whole front of some apartments at S. 23rd and S. King Street in Seattle.
Yesterday I was in the area and remembered them and took a few shots.They look like this Rubus.When do they flower and fruit,as these had neither? Thanks,Brady
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Notice how different these last are from the previous photo. These last are the more common one, the one that is apparently now being called Rubus hayata-koidzumii by at least part of the botanical community. I don't think flowering occurs this early in the year, but I don't remember. The orange fruits I do remember being seen later, as in summer.

They definitely look different. I quite like the look of the more common one. For what it's worth, mine flowered in the summer, but as mentioned above, they have never produced fruit. I may try watering some of them this summer to see if that helps.

It turns out these plants are more common than I thought.
I saw these in sidewalk plantings all over the Trilogy area in Redmond,WA and it's the first time I tasted the fruit.To me,it resembles Salmonberries,maybe a little more intense and seedier.
It also is growing in a bed along Redmond-Fall City Highway near East Lake Sammamish Road. Brady

Thanks for the prompt. I had been meaning to photograph some neighborhood plants all summer.

Nice pics Larry.Those are loaded.I have a feeling they like them well trimmed in Trilogy.