Yes, it's time if flowering. Not many grow blueberries in this forum. I do, but no where near you. You can ask in the Orchard forum where dozens and dozens of people grow them in ground and in containers.
Usually you start fertilizing when they begin to grow. What cultivars are you growing? Use only acidic fertilizer too. Blueberries are sensitive to nitrates and have limited ability to absorb them. Acid fertilizers use the ammonium form which blueberries love. I use cottonseed meal, Holly-Tone, or Ammonium sulfate, but you have to be careful with it.
No more than 1 tsp per gallon, I use about 1/2 if using. I like this fertilizer because it is also very acidic. PH is super important to keep right for blueberries.
Follow label instructions on organic fertilizers. usually twice a year. With Ammonium sulfate about once a month. You will need to use this as a supplement as it only contains nitrogen. So I like to use an organic twice a year and use an acidic soluble once a month at very low doses.

Yes, I didn't know where to ask the question so I started here. I'll also take a look in the Orchard forum.

I've started using Ammonium sulfate in low doses and I occasionally use what used to be called MirAcid. And I have some Espoma soil acidifier (30% sulfur) that I've been sprinkling into the containers. I'm not sure how often I need to do that, but I'm about to start the year with some. Lastly, when I think about it I add 1 tbsp of vinegar to each gal of water that I use for watering the blueberries. I try to do this every third time I water.

Cultivars that I have:

Paloma
Jubilee
Emerald
O'Neal
Southmoon
Misty
Sunshine Blue
Sharpblue
Star
Sweetcrisp

Some in 15 gal, some in 5 gal.

I've also been using the Ammonium Sulfate for citrus, in containers and in-ground. It's really brought some old in-ground orange trees back to life. For the citrus I'm using 1 tbsp per gallon water, with blueberries I use less (1-2 tsp).

Thanks for the advice, I'll try to get into the habit of feeding the blueberries once a month.

John

Wow, you have a lot!! OK, I feed AS once a month but supplement with organic. So you probably could use it more often. Remember too that AS is only nitrogen they need potassium and phosphorous too. The Miracid gives that. If they look good keep doing what you are doing. The soil acidifier takes 6 months to work, so keep that in mind. You could over do it. Follow label directions. The vinegar in water is a good idea too. I myself use sulfuric acid. But in pots vinegar works well. In ground Sulfuric acid is better.
Vinegar only temporally ties up carbonates to make it acidic. Bacteria break it down in about a month. In pots though the tied up carbonates are flushed when you water, so they are removed. In ground they stay, so vinegar doesn't work well there.
Keep us updated, and any photos would be cool too. I have Sweetcrisp and Southmoon myself. Most of mine are Northern, which would not work for you
Some other good ones Southern highbush are Santa Fe, Springhigh, and Springwide.