It is incredibly variable. In the wild seagrass has noticeable seasons with faster growth seeming to occur during warming and cooling trends, spring and fall.
I want to say that it does not by any means grow slowly for me. Thalassia excluded in this remark though. Halodule, Halophila, Ruppia and even Syringodium are throwing out about five or ten plants per day in a 10x10" bed. You need to start with healthy material and give it the nutrients it needs to grow. If its hits a limiting factor, growth will slow or stop.
Adding in CO2, adding ferts (NO3 5-10, PO4 0.1, Fe normal dosing) is all very very key. This is how I have maximized growth rates so far. And I also wanted to mention that substrate only plays a big factor in my tanks that I have tried to setup to not need fertilizing. The plants get by on the fish bioload and whatever they can get from the substrate. They grow very slowly in these environments in comparison to my supplemented/dosed tanks. Those tanks have nothing but plain aragonite. I think you could get by with plain silica sand in fact in that style of setup.
The fastest growing grass seems to be Halophile engelmanii for me, shoal grass is a close second. Slowest is definitely turtle grass, but I'm not sure that's fair of me to say. The smaller species of grass - star, oar, shoal, manatee - are somewhat similar to annual plants. They pop up every year from seeds and dormant rhizomes and they die back in cycles. I havent experienced that so far in my tanks though. Turtle grass is more like a perennial plant that grows and grows and grows.. but is around for a very very long time.
Anyone else have similar experience? Or a different perspective?
>Sarah
