wouldn't a high phosphorus fert. make them flower like crazy? maybe you need enough phosphorus, but not too much.

I'm afraid I don't have much to offer in the way of advice on this. But I had to comment because of this statement:
"we've just had a very cold winter by subtropical standards. There was a whole month where it was less than 50 degrees F (10 C) outside."

50 degrees?! You must live in paradise, kea2!

As plantboy said, phosphorous will push the plants to bud. But it's also likely that they are just old plants. After a few months, basil will go to seed no matter what you do. You have to plant new seeds every 2 months or so and kill the old ones if you want a continuous crop.

I don't know a thing about chinese basil, but with regular basil you absolutely have to snip the flowers off before they bloom if you want them to have good flavor. IMO you should toss those plants and start again. You could pick the leaves and dry them, but the flavor is weak once the flowers open :(.

Hey, 50 degrees F is no picnic when all the houses are uninsulated, unheated concrete boxes. I've spent winters in Boston so I know the contrast. In Boston you suffer intensely in short bursts and then go inside for relief. Here, you suffer moderately all day long, indoors and out. It wears you down.

Oh well, I guess I'll have to eat these plants and grow new ones. And after I spent so much effort trying to keep them alive. *sigh* I think I'll go back to dirt. Apart from my mint, all my experiments in hydroculture haven't gone very well. I'm too poor to afford the good equipment.

Don't give up! Plant some semi-head lettuce (like bibb or Boston lettuce) in those same containers. They will grow like wildfire and give you renewed confidence.

One thing though. How are you putting oxygen into the water/nutrient solution at the bottom of your containers? It's not clear from your photo, and it's very necessary for good plant growth.

I just stir it every other day or so. And blow bubbles in it with a straw.

Hi Kea,

I have been looking at your pictures, and I think your problem must be the nutrient. Check my son's herbs:

{{gwi:1001581}}

Nothing wrong here! But I think the difference is that we make our own nutrient. Also, the plants stay outside all day, all year. (lowest temp in winter ±10°C; highest in summer ±40°C)