As others have suggested, a lot of it may have to do with growing degree days in your particular Zone 6 region; in other words, you may have a considerably cooler growing season than some other areas designated zone 6 on the basis of average winter lows.
This is my second year with in-ground figs here in 6b Kentucky, and the Hardy Chicago/Mt. Etna family figs started ripening the first half of August, with Malta Black being just a smidge ahead of the others, placing it neck-and-neck with Improved Celeste (my current favorite) here. I think your HC will probably catch up with a little more time and maturity. Olympian should catch up, too. My in-ground Olympian started ripening main crop on 9/13. No brebas here; but, of course, all my figs were cut back to 2â-3â stubs for overwintering.
Another thing I noticed this year: those located in microclimatesâe.g., against concrete or near small bodies of water or other objects that collect and release thermal energyâstarted ripening a little earlier than those that arenât. (Not surprisingly, figs in microclimates also had better survival of wood over winter.) If yours are not in such a locationâand moving them is not an optionâmaybe you can create a similar effect by stacking rocks or concrete blocks or even placing black-painted drums of water near them. Iâve also heard reports that warming the soil with black groundcloth or plastic in the spring can hasten the season in marginal zones. Itâs something I hope to experiment with next season.
I find it curious, on the other hand, that your green main crop figs are not merely failing to ripen, but are actually aborting. This would not be surprising with old-fashioned Celeste, but I wouldnât think HC and the others would so readily drop unless the trees are in some manner stressed. Now, I have had some unripe figs drop in the last week or soâbut that is almost certainly attributable to water stress: weâre now in drought conditions and everything is bone-dry. Hand watering and mulching my figs has helped somewhat (unfortunately, my figs are located in areas that make regular irrigation by hose difficult) but the surrounding soilâand airâis so hot and arid, that theyâre still awfully stressed, and as a result theyâve dropped a lot of stagnant figs; Olympian is especially hard hitâand probably more so because itâs in especially poor/dry soil, and Iâve been under the weather for the past couple of weeks and have had a hard time keeping up with watering. Are your figs getting steady moisture during late summer/early fall? Also, is there some nutrient that could be lacking? Calcium deficiencies, for example, can increase green fruit drop in some trees.
As far as big-fruited figs that will make it, you could look into Longue dâAout (which may be the same as Nordland). My in-ground came through the winter fine (with protection) but I culled it before it could crop and am replacing it with healthier (i.e, FMD symptom-free) specimens. There are reports of it growing and producing well in ground in 6/7. Others report Yellow Long Neck as fairly cold hardy, but Iâve not heard of anyone actually cropping it in ground in 6/7. My YLN, a tissue culture, came through the winter with very little damage (protected on a south-facing sunny slope, just above a little partially filled in pond/swampy area); so it definitely has potential survival-wise. In terms of figs, though, it produced nada this seasonânot even a double-bump. (Maybe itâs one of those uncooperative TCs? Iâve just propagated another from a cutting to see if I can get it to fruit next year.)
Anyway, just a few thoughts based on my very limited experience. Good luck!