I'm not sure if you have this variety over there - but last year I grew cucumbers called 'Lemon Crystal'. The fruits were round, yellow, but the flesh tasted great - just like regular cucumbers. Plus, you don't need to remove the male flowers as this variety needs to be fertilised to set...
Add some lemon juice to your jam.
Some fruits don't have pectin in them [or not enough] This is the stuff that you need in order for your jam to set.
You can buy pectin from stores [well here in the UK, you can] - or you can add another fruit or juice from a fruit that does have it in...
It is either a wallflower, or Stock.
Stock:
Wallflower:
Both plants are biennials. Grow from seed one year and flower the next. During mild winters, it i possible to keep them going for longer than the usual 2 years, especially if you have dead-headed them often.
Interestingly, the 'Rose of Sharon' has been attributed to other plants as well.
http://www.ehow.com/about_6756843_rose-sharon.html
Best to stick to the proper names of the plants, not the common names. Your plant remains a hibiscus.
Rose of Sharon IS a Hibiscus!!!
Well, according to this site it is, anyway:
http://treesandshrubs.about.com/od/commonshrubs/p/RoseofSharon.htm
However, here in the uk, your plant would be a Hibiscus. Rose of sharon is a Hypericum - as seen on this web page...