Your plant looks really healthy. My instinct says to pick a cornichon off every couple of days or so. The plant will want to produce.

Its hard to tell what kind of sun exposure your cuke is getting (cukes love sun and heat). Maybe the cold spells have set her back? Good luck!

When the fruit doesn't fill out properly and falls off, it is usually one of two things happening.
1- the fruit isn't getting fully pollinated and therefor drops off. (not all varieties require pollination to develop fruit but most do.) If this is the problem, you could try picking a male flower (the ones without a little cucumber behind it) and pull the petals off and use it to pollinate the females.

2- If the blossom end is turning brown and soft before the fruit drops off, it could be Blossom end rot or (BER.) BER is a calcium deficiency in the growing fruit. It is quite common in tomatoes but also attacks other fruiting plants especially squash I've noticed. Anyway, it might not be a lack of calcium in the soil since any root stress can often stop the roots from being able to take up enough calcium. Or if the plant is just growing soo fast that the plant just can't get the calcium to the fruit fast enough to keep up. They make BER spray that you can foliar feed with to help the plant get the calcium where it needs it quicker. Some plants outgrow the BER problem if it is just from growing too fast and it is just the first few fruit that you loose. Once a fruit shows signs of BER, you can't save it all you can do is try to improve conditions for the plant to produce future healthy fruit.

Good luck, looks like a nice plant.
Is it just one plant......
There could be a 3rd option. If that is one of those types of plant that only produces female flowers (and isn't parthenogenic which means all female flowers capable of producing fruit without pollination) but requires cross pollination from another plant that has male flowers. In which case, you will need to find someone with another cucumber plant that can give you some male flowers to use on your girl flowers.

Has it been doing this very long? Female flowers mature faster than the male and it's not unusual for the first few incipient fruits not to get pollinated. Time may cure the problem as the male flowers come along.

Sounds like you should try to hand pollinate and see if it helps

i agree with cjc.

I agree, sounds like lack of pollination. Get a pack of small artist brushes from HD in the Paint Dept. and start hand pollinating. It will be obvious with the zukes, doubtful you'll be able to see the pollen during transfer on the cukes but it will still solve your problem, unless you bought a gynoecious variety that might be lacking any male pollinators.

Tom

Wow, lots of good ideas, thanks everyone. The plants, there are 2, are growing in a single bucket 5 gal SWC with the 45%peat,45% cow compost (by the way Tom there is not a measurable difference in the soil temp between the compost mix and the pine fine mix), and 10% perlite. Can not remember if it got 14 14 14 Nutricote or 6 6 6 chemical fert without being down in the garden. It was grown from a burpee pickler seed pack. No mention on pack about pollination. It is in full sun.

CJC sez; Has it been doing this very long? Female flowers mature faster than the male and it's not unusual for the first few incipient fruits not to get pollinated. Time may cure the problem as the male flowers come along.

This may be the answer along with the cold snap because 3 or 4 of them are now past the withering up stage (3 inches long). I will try to identify if it has male and female blossoms tomorrow.
They have really been growing fast , but I'm newbie and do not know how fast is fast :>)

Happy Easter,
bernie

Pollination can't be the problem if you have baby cukes falling off, right? It sounds like you have pollination going on. It is normal fot the male flowers to fall off early.

Could you perhaps be overwatering? I'm not an expert by any means, but I'm growing cukes by pot and gound and water only in the morning, harvest every day or so. The pot cukes look like they're begging for water by evening, all wilted and pathetic looking.

Good luck, hope you have happy cukes soon.