Hi Suzanne,
I am new to this site as well, but not to plants. Duke is a very nice variety. Here is info I found for a research paper I did in the pass

Plant Description:
4 to 6 ft. at maturity. Ripens July 1 in zone 5. Yields 10 to 15 lbs. per plant. Medium size berry of excellent, firm quality. Ships well to fresh markets. Berries are borne on long stems and loose clusters, making for easy harvesting. Has adapted well throughout the United States and is very popular with growers.

Chilling Hours:
700-1200 Hours

Hardiness Zone:
Zones 5-8
Northern Highbush
Blueberries don't self pollinate (sp?) So if your friut is small you will need to get another variety. Not 50 plants worth maybe 10-15 to inter plant among the Dukes. A few examples would be: Bluetta, Blue Haven, Blue Ray, Caroline, Chanticleer, Collins, Denise, Earliblue, jst to name a few. Pruning is also important. You want to remove the old canes that aare no longer produceing and remove all but 2-3 young canes. This will help with growth control and disease and insect problems. Fertilizing can be tricky. Get a soil test done. Make sure your soil is between 5.0-5.5 oH. They perefer sandy like soils but moist. They are bog loving plants, with light soils. I feed with a slow release acidc fertilizer 2-3 times a year. You don't wont t much fertiler you will burn the roots. They are shallow rooted, this is why they need alot of water and fert.The fertilzer I use has micros in it as well. I also inject fert it the irrigation system about once a week. Start with the sloe release if they don't seem to put on new growth then inject some fertilizer into you irrigation lines. If you have any more questions please let me know, I will try my best to answer them for you. Marie
PS I know I have all these degerees and still can't spell. It doesn't help my brain works faster then my fingers can type. I am sorry for any misspelled words or incorrect grammer. :)