after the first leaf is formed? Some of my blueberry sprouts failed because they didn't come out of the seed coat.
This will be the reasoning behind drastically overplanting. Most of them will fail, and there is nothing that you can do about it. This is natures way of culling out unfit genetics.
Think of it this way... Helping the little guy out of his seed for him may help him to survive, but if the genetics are unfit, then it may be more trouble than its worth to keep it alive. It will likely be nutrient deficient, prone to infection, and not very strong. Continuing on a genetic line unfit for survival can prove disastrous for species in the long run, though breeding.
This article will help you to grow blueberry plants: https://www.gardeningknowhow.com/edible/fruits/blueberries/growing-blueberry.htm
There were still many berries but they wouldn't get big like the earliest berries. What should I do to continue large berries? Tons of berries on the ends of branches stayed tiny.
If you don't fertilize with blueberry fertilizer regularly, then will likely be the issue.
Here is an article that will help: https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-fertilizer.htm
Blueberries have always been larger than this year.
You didn't mention whether you're growing your berries in a garden or in pots. It is thought that if you plant a few different varieties rather than one kind, the berries are likely to increase in size.
This article contains quite a bit of information about properly caring for your blueberries:
https://www.gardeningknowhow.com/edible/fruits/blueberries/growing-blueberry.htm
https://blogs.cornell.edu/berrytool/blueberries/blueberries-fruit-are-small/
How late in the year can large blueberry shrubs be trimmed?
You are in Zone 7B. Our experts say the best time to prune blueberries is in late winter to early spring (January to early March) after all chance of severe weather has passed. Read more here: https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-plant-pruning.htm
is it caused by something else? I don't have a pH meter so I tried using rockwool media and made it sour with regular vinegar.
Vinegar should be used very carefully, and with a pH meter. This is especially true since it is toxic to plants. Citric acid is a much better alternative. Seedlings nor young rooting cuttings can handle acetic acid so vinegar is not to be used in this situation.
In your situation, and not having a pH meter, it will be best to start these in soilless media that is already pH balanced, and DOES NOT contain nutrients. Nitrates of any kind should NOT be used on blueberries.
What you are seeing is stress from toxicity, and probably low pH. I would transplant these into a seedling starting, or inert soilless blend as soon as possible. Do not feed until it is showing new top growth. Then feed it with something made for blueberries, since you do not have a meter to adjust the pH properly.
This article will help you to care for blueberries: https://www.gardeningknowhow.com/edible/fruits/blueberries/growing-blueberry.htm
This article will help you to propagate cuttings from them: https://www.gardeningknowhow.com/edible/fruits/blueberries/how-to-propagate-blueberry-bushes.htm
They are in large pots (60 cm) and have cropped poorly but blue for the last 5 years. Ericaceous soil and feed and rainwater. Weird but the blackbirds won't touch them this year. All berries are scarlet. Help
Hm. This is usually caused by a pH issue, but If you are using acidic soil and fertilizers, then I would check to make sure that the mix does not contain any nitrates. This could definitely be ammonium nitrate damage.
Blueberries need, not only, acidic soil but they also need ammonium sulfate, rather than ammonium nitrate as a nitrogen source.
Be sure that you are feeding with a blueberry fertilizer, or one that does not contain nitrates.
These articles will help: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/edible/fruits/blueberries/grow-blueberries-in-pots.htm
Although there are plenty of references on the web, most do not illustrate well enough for me to understand or execute
When to prune depends on the type of blueberry that you have, highbush or lowbush. They can get unruly, so removing large unproductive branches and any lower growth touching the ground would help. This article will get you started: https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-plant-pruning.htm