How long can a mix of liquid fish and seaweed be left in a spray
bottle? How often should it be used as a foliar spray on
vegetables?

Any type of tea like this can be left in a bottle for months.
But keep in mind that any non-aerated tea made from any organic proteeins or carbohydrates will have no beneficial aerobic microbes living in it. It shouldn't be used as a foliar spray at all. It is too risky.

Most stinky non-aerobic tea solutions are best used as a very, very, weak soil drench or as a compost pile activator.

Happy Gardening!

What do you mean "risky"

Most fungal diseases on plant foliage and in the topsoil, are formed via "anaerobic" microbes. Almost 99% of all beneficial microbes on plant foliage and in the soil for organic and sustainable gardening are totally "aerobic".

Personally I would never use anything anaerobic on my plant foliage, except aerobic aerated compost tea recipes. Now there is nothing wrong with mixing any form of liquid fish and seaweed products in a good aerobic aerated compost tea recipe. That way you have the best of both worlds: The best organic plant and soil fertilizers, and the best colonization of aerobic beneficial bacteria and fungi and other soil microbes for disease control and good organic soil management.

If you use any type of non-aerated anaerobic organic liquid for gardening (foliar spray or soil drench), make sure it is very, very diluted and not too strong.

With aerobic aerated teas you don't have to worry too much about the dilution ratio, as long as the tea is diluted to a very light color, and has a pleasant wine or yeasty smell. This is a noticeable sign of a great colonization of aerobic bacteria and fungi in the aerated tea recipe.

Happy Gardening!

I have used Bioform for many years, as a foliar feed and for root feeding. It is fish and seaweed emulsion and works great. I mix it up and use it all throughout the growing sason on all indoor and outdoor plants. Roses love it.

Captain? How about seaweed? It's been used successfully as a foliar feed for a long time.

I agree totally. I use homemade non-aerated seaweed tea recipes in my foliar teas all the time for extra nutrients and for stress relief for plants.

I just like to use aerobic compost tea recipes as an extra assurance policy against potential plant and soil disease issues. I sometimes add non-aerated anaerobic fish and seaweed solutions to my aerobic tea brews for extra protein and carbohydrates for the beneficial soil microbes to digest.

Any type of diluted liquid natural fertilizer or soil activator should be used with moderation anyway. After good composting , mulching, and cover cropping techniques, using any form of protein/carbohydrate fertilizer should be secondary, and used as needed.

Happy Gardening!