How strong does the agar have to be?

[Tindomul]

When making flasks, how concentrated does the agar have to be? I made mine at 15 grams per liter of water, I found that 10 was just not good enough to solidify. So now I am wondering if my failed protocorms died because my agar was too thick. I wonder if my seeds would have done better at 13 grams per liter.

[Royal]

I've only used premade media with agar already included. But from what I remember from discussions, 7 g/l is about standard (+ or -). I may be wrong here.

I doubt the stiffness of media would affect germination, but I may be wrong here too. I have had a few batches that didn't gel like I wanted them to, and a few where it was too stiff. I attributed that to poor mixing while dispensing and/or not fully dissolving all of the agar. Since I've made it a point to get it good and hot and stir frequently while dispensing, I haven't had another problem.

[Tindomul]

7 grams per liter!!! There must be something else in that mix that helps solidify. For me 10 grams will not solidify, even in the fridge!

[Royal]

There are different grades (purity) of agar. Where did you get it?

[Tindomul]

Fisher Scientific.

[Royal]

My only guess is that it didn't get fully dissolved or was a bad batch. Again, I may be way off on the strength but that's my recollection.

Did any of the flasks gel? Did a portion of each (like a layer at the bottom) gel?

[Phalguy]

I have used agar at 6 gr per liter with good success...
I use premade media now!

[thegardener]

Originally Posted by Phalguy

I have used agar at 6 gr per liter with good success...
I use premade media now!

Yeah, from 6 to 8 gr per liter is good enough to get a thick medium. Maybe your problem is the heating.

[Tindomul]

I can't imagine that would be the problem. I'm using an autoclave.

[Royal]

Are you autoclaving the entire batch in one vessel, or dispensing then autoclaving? If the medium doesn't get hot enough to fully dissolve the agar, it gets unevenly dispensed into the flasks. You wind up with a super thick layer at the bottom of the last few flasks and the rest are watery.