They need plenty of water with mulch over their shallow root systems. Also need full sun and yearly pruning plus fertilizer.

See "Growing Blueberries in Your Home Garden" - https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec1304.pdf

Peat should never be used as a mulch. When it dries out, it repels water and it is very hard to wet it again. If the soil needs to be more acid--and you can't know without a soil test--use soil sulfur to acidify it (not aluminum sulfate).

The comments "shallow root systems" and "Peat should never be used as a mulch" have led me to extend my original question. I now feel that I didn't prepare the original planting site well enough (didn't know enough about blueberries at the time) and so have decided I need to dig up the plant, prepare a much larger hole for it, including conditioning the soil by adding Peat Moss and lots of compost, and then replant it. Question is: should I do that now while it is dormant (my ground doesn't freeze) or in March/April when it starts to bud and is ready to begin growing again?

Also, make sure you have more than one variety. Blueberries are not very self-fertile, so a mix of different varieties is recommended. If you have flowers but no fruit, that may be the problem!

Do you have rhododendrons or azaleas? Same site requirements - I wouldn't do anything to the blueberries that hasn't been necessary for these flowering shrubs to perform acceptably for you. Except for planting at least 3 different blueberry cultivars, in order to cover cross pollination requirements.

And in general amending of individual planting hole back-fill for long term plants is counterproductive, due primarily to how amending of planting holes affects the movement of water into and out of the treated area. This applies to any situation including small beds or strips where the plants will be placed in a small amended area surrounded by a much larger zone of unmodified soil.

There is also the problem of settling of amended soil as organic amendments decompose and disappear, resulting sinking of specimens planted in it.

Finally even for vegetable plots the percentage of organic material contained by the soil actually needs to be rather low or there can be problems.

The Myth of Soil Amendments, Part III
“Healthy soil has high organic content”

https://s3.wp.wsu.edu/uploads/sites/403/2015/03/soil-amendments-3.pdf

Embothrium, very interesting comments! Incidentally I have a rhododendron about 4 feet away and it flowers very well every year. However, my blueberry, which was a 2 year old plant when I planted it, did not even flower in its third year, and of course no flowers then no fruit.

I have the new hole almost dug so I am going to continue and transplant it. I didn't plant the rhododendron so I have no idea what was done for it when it was planted. However, I do know that I didn't do a very good job when I planted the blueberry and so its spot is mostly sand and large rocks - probably no soil whatsoever other than what was in the original 8" pot! Shame on me I know! I'm trying to do better this time.

It will like the sandy soil if you keep the blueberry mulched and watered (during dry spells) after planting. Except for those that grow in peat bogs in general heath family plants are found on sandy or otherwise well aerated substrates in nature. Consistent with this a now closed longtime garden center near me had high-bush blueberry* plants come up wild on an old conifer stump there, that was getting hit by sprinklers during the watering of the nearby potted nursery stock. Just as the locally native red huckleberry and salal do, in this instance under natural conditions without irrigation (high-bush blueberry is an eastern North American species adapted to eastern summer rainfall regimes).

When you pop it out try plunging it in a tub of clean water to see if the original potting soil bubbles much, plants installed with their roots in undisturbed soil-less potting medium often have a problem with this material shedding water to the surrounding soil in the planting hole. Even during humid or rainy conditions.

*Same species you are trying to grow, if it is the familiar grocery store fruit