The reason you're not getting fruit from Arapaho is because it needs roughly 500 hours of chill. I highly doubt that you ever will get that many hours given that you're in zone 10.

There aren't any thornless primocane fruiting blackberries yet, but they are on the near horizon as there are advanced selections in the UofA program that are thornless and primocane fruiting.

The erect types from the Arkansas program usually fill in rather well (at least production fields I've seen). They're usually planted closer (2-4 feet apart) than a trailing type (4-8 feet apart). However, the thornless erect don't sucker from roots quite as easily as the thorny types.

Have you ever gotten any blackberries to fruit for you? I'm curious to know what they are if you have.

No, I have not gotten blackberries to fruit. I had one VERY erect, very vigorous, thorny variety I planted some years ago that I bought at OSH (OSH rarely) label their varieties correctly, so it's irrelevant. It took over my front yard and my neighbor's yard before I decided I didn't want to deal with the thorns long enough to wait for any fruit.

This is one reason that I am so disappointed with Arapaho. I figured that if it was anything like the OSH blackberries, it would be a breeze to let it self-propagate, and it would be thornless, too. That's the one trait I would really like. Vigorous self-propagation, although not necessarily as vigorous as my mystery OSH blackberry.

The problem with the Arapaho isn't that it hasn't fruited. (And, no, it hasn't). The problem is that it isn't growing or spreading very well, and it has had quite a bit of time. This last January, after one of our frosts, the leaves died, so I chopped off all branches, in hopes that I might get some decent new first year canes. The old canes on the three plants were, well, about two feet tall and weak looking. Miserable looking little things. Tomatoes and basil and lettuce and yerba buena thrived on all sides of it.

My everbearing raspberries (OSH, unlabeled) have born fruit every year since I started them, blooming in Mid July and fruiting through to Christmas. They have spread like wildfire, even coming up in the cracks between the sidewalk yards away.

My ex-father-in-law has thorny blackberry bushes that produce every year on the on second year canes, and he lives only a half mile from me, so I don't think southern California is blackberry-proof.

I just looked up my chill hours. I had no idea that chill hours were a concern with commercial blackberry varieties.

Long Beach, California: 489 hours below 45 degrees. 462 hours below 45 but higher than 32.

Here is a link that might be useful: Chill Hours

Triple Crown supposedly bears well in zone 10 SoCal. I'm in Maine, much different climate than SoCal. I have Triple Crown. They spread so quickly, they should be considered invasive. You can plant one plant, and in a few years you could have several hundred spread out 40+ feet from where it was planted. They're not primocane, and you have to search for the berries since they're usually hidden under lots of leaves. Good for kids to have fun while picking. The canes are fairly erect for the bottom half, while the tops hangs down. They might grow differently in SoCal.

I'll put Triple Crown on my list of berries to try then. :)

About berries in southern California... I would never have dreamed it would pose a geographical issue, the way cherries or apples do. Some of my fondest childhood memories are of picking blackberries in Griffith Park in L.A. and missing school from the runs! And, of course, there was always Knott's Berry Farm in Anaheim, about a 20 minute drive from here, which is an amusement park now, but it was still a berry farm and stand when I was a kid, renowned for their boysenberries.

Aha! More googling reveals something else I thought I remembered. Old man Knott developed the Boysenberry. I can smell their candy store now... Knott's was something else back then, more of an old West museum than a roller coaster park.

Wikipedia entry on Boysenberry

More cool stuff about Walter Knott

Another google search reveals there is a beast called the California Blackberry (Rubus ursina), alleged to be one of the progenitors of the boysenberry, although wikipedia doesn't mention that. Supposedly a very tasty but sharp wild blackberry. Perhaps that is what grows wild in Los Angeles parks.

Okay, back to business. I like the idea of an aggressive, thornless berry like Triple Crown. Are there any other aggressively-growing thornless blackberries that might do well in southern Cal? Preferably ones that aren't trailing?

If I can collect a few worthwhile names to try, I'll order some and let them battle it out for supremacy.

Rubus ursinus grows wild all over the PNW, including northern California, but I never would have guessed it grew in SoCal too. Creeping, with thin canes that spread over the ground and work their way through trees and shrubs. Fine hair like thorns you don't notice right away but work their way into your skin and then you can't get them out again. Small berries late spring that are the absolute by far best blackberries ever. Most people around here call it the 'little wild' blackberry to distinguish it from the invasive himalayan blackberry, Rubus armeniacus. Huge arching clambering thick canes with fish hooks for thorns. large tasteless berries in late summer.

Fine hair-like thorns? Like raspberries? The blackberries in Griffith Park have the more traditional rose-like thorns. They grow in large tangled messes about 3 or four feet tall and however deep. Lots and lots of spider webs, too. It was probably not ursinus, I guess.

I did some more researching... The Wikipedia entry on blackberries had some interesting background on the development of the thornless varieties. The thornless-erect varieties have been developed (primarily) at the University of Arkansas, and they share some common traits, including that they are "less vigorous" but tolerate cold better than the semi-erect varieties. (Navaho, Ouachita, Cherokee, Apache, Arapaho and Kiowa.) They propagate through root runners.

Many of the Eastern semi-erect thornless varieties were developed through USDA-ARS in Maryland and were hybridized from the UK's Merton Thornless. "The semi-erect blackberries are thornless, crown forming, incredibly vigorous, and need a trellis for support. Cultivars of this type include the very popular Chester Thornless as well as Triple Crown, Loch Ness, 'Loch Tay', Smoothstem, Hull Thornless, Dirksen Thornless and Black Satin."

Many of the trailing varieties have been developed though USDA-ARS's Oregon facility. (Black Diamond, Black Pearl and Nightfall as well as the very early ripening Obsidian and Metolius.)

The erect ones tend to be the most cold-hardy, the trailing ones the least.

I am having the greatest difficulty finding information about chill hours for blackberries. Not a clue to be found, anywhere. It would be nice to have all this in a convenient blackberry FAQ.

I thought I researched the subject of blackberries fairly well before ordering the Arapaho, years ago. I've been patting myself on the back for being so thorough in picking the best variety... and then I waited, and waited, and waited. From reading older threads on the forum here, I can see now that there are many people that have had problems with Arapaho just "not growing" after being planted, so my problem is not unique. Why? I don't know. Maybe the UofA thornless plants have more temperamental soil or climate requirements than the other thornless varieties. I read one article last night about experiments growing commercial varietes in Arizona, and the worst performing of the lot were the UofA varieties. The Texas developed varieties performed very well. Key quote:

"Most of the blackberries planted had new shoot growth three to four weeks after planting. Up to three plants of each variety did not have a growth flush; these plants had all died by summer 1994. All the plants of the 'Arapaho', 'Cherokee' and 'Shawnee' cultivars had died by spring 1995. All the plants of 'Cheyenne', 'Choctaw' and 'Navajo' cultivars had died by spring 1997. We attribute the mortality to lack of chilling. Arkansas varieties apparently do not grow well in southern Arizona because of the warm winters, as suggested by Moore (1984)."
Arizona article

(Dr. Moore is the man behind the whole UofA breeding program for the past 40 years.)

I guess I made a mistake going with Arapaho. Such a shame, though, to have to find out this way. Three years wasted. It looks, now, as though I would have been better off with semi-erect thornless varieties (like Triple Crown) that were developed at Maryland.

Does anybody have any leads on chill hour requirements? It would be nice if we could make a table.

I have a copy (not PDF, unfortunately) of a recent article that was published in the Journal of the American Pomological Society here's the citation:
Carter, PM, et al. 2006. Chilling resplonse of Arkansas blackberry cultivars. JAPS 60(4) 187-197.

When you read the article, it becomes clear why the chill requirement for different varieties isn't all that understood and defined. However, here's what it says in general:

Arapaho 4-500
Navaho 8-900
Choctaw believed low
Kiowa 2-300
Shawnee 4-600

No research has been done on the trailing types from Oregon or the semi-erect types, but they are generally believed to be high.

I'm not surprised the Texas blackberry cultivars did well in Arizona. Unfortunatley, that program hasn't been active in years. There are breeding efforts in Brazil and Mexico now, though, that focus on heat-tolerant low-chill cultivars, so maybe something will come out of there that homeowners here will be able to get.

And a final note, Dr. Jim Moore started the breeding program at Arkansas, and it's now under the direction of Dr. John Clark (since the early 90s, I think). Dr. Moore was still heavily involved up to about 6 or 7 years ago, but unfortunately has health problems now that prevent him from being so involved.

My Arapaho promptly died the first season that I planted it. In its defense, it may have been in the same location where my black satin died so there may be something wrong with that spot.

My other varieties seem to be doing quite well. Loch Ness, Nightfall, ORUS 1843, Triple Crown, and Apache.

Apache, being and erect, has a very clearly different growth habit than the others. It is considerably less vigorous, has larger leaves and is upright.

According to that list Nightfall is trailing and Loch Ness is semi erect. I'm not sure what semi-erect is supposed to mean, but the growth habit between them isn't much different.

The growth habit of the Loch Ness is certainly much more similar to the Nightfall than it is to the Apache. In the 3rd year the Apache is very contained with minimal pruning whereas the others seem that they could cover a lot of ground (and trellis) very quickly if not kept in check.

The trailing and semi-trailing were also very easy to propagate by tip-rooting. I just stabbed a hole in the mulch/dirt, poked the end of a long primocane in it, and in some cases weighted the stem down with a rock to keep it from being disturbed.

I now see new primocanes emerging from the vicinity of where the tips were buried.

I'm sure any of these semi-erect varieties would fill in you space more than adequately within a few years.

Have you considered the thornless boysenberry? We grew some in a school garden, and it did well in the North Hollywood area of Los Angeles, produced large black berries, was somewhat invasive. One of the children called it the "poisonberry" plant. The children always beat the adults to the ripe berries, so I never was able to taste one.

That is impressive how much chill Long Beach got this winter. Coastal Ventura county had only 300 or so, Santa Monica 80. It was definetly not a normal year for chill, much colder. DO NOT TRY BLACK SATIN! It was horrible tasting. I riped it out and am trying a plant someone gave me. I think its triple crown. They are in zone 10 and it fruits well, and tastes great. It is thorny, and a vining type.

University of California Cooperative Extension has lots of fruit growing information on the web. Most varieties (including 'Arapaho') listed in previous edition of Sunset Western Garden Book zoned for your area. Under 'Arapaho' it says "'Apache', 'Chickasaw', 'Choctaw', 'Kiowa', 'Navaho', and 'Shawnee' are similar varieties. All grow well in hot-summer climates."

I have been researching the blackberries for Albuquerque and found an article from AZ that reported the variety of "Rosborough" to fruit well in hot climates. Want the article?

Hot humid low-chill New Orleans.

Arapahoe, Natchez, Cherokee, Choctaw, Navaho refuse to even grow here, much less bloom and bear fruit.

Brazos grows and fruits o.k. but with many small berries.

Kiowa, Ouachita, Triple Crown, Prime-Ark Freedom (somewhat everbearing) all grow, thrive, and fruit like there's no tomorrow. Dream varieties. I have 3 more great varieties, but grass cutter threw away the labels. One of these three is known to be 'Sweetie Pie', but which one? The best one of these 3 makes many blooms over a LONG period, and it produces a few berries ALL year long. So far, too, it's the BEST tasting one of all my varieties, and it sends out runners EVERYwhere.

By the way, someone speculated that their unlabelled t-h-o-r-n-y variety was likely Triple Crown. Sorry, but that variety is thornless.

Thorny or thornless doesn't matter to me. Even in sweltering weather here, a long-sleeved shirt, long pants, and gloves make a world of difference to me. To me, the final berry product is what matters. It's the ONE AND ONLY thing that matters!