How does loosestrife spread? By seed or by roots? Can you control it by putting it in a pot and then planting the pot in the ground if it spread by roots.

It spreads by roots/rhizomes. The roots creep under and sometimes over obstacles and then sprouts from where ever the roots grow. They are pretty aggressive. I have never tried planting them in a container and burying it, however I am sure that would keep them in check.

Maybe...if the bottom five inches of the pot was solid cement. It's determined to spread.

Thank you Shade and Pirl. If I ever get the chance to try Loosestrife, I will give it a try in a pot planted in the ground.

I think it also spreads by seeds, so you would also need to deadhead the flowers to keep it from spreading.
I had one plant show up in my yard even though there were no others around.
I expect the seed came in a mix.

Ours only spreads by those endlessly energetic underground rhizomes. This is very valuable information for those who have never grown it:
http://www.missouribotanicalga...

When I get to digging out more of it that strayed, I'll take photos of the root system.

I have never had them spread by seed either. Those rhizomes are pretty tenacious though.

I have read it is edible. I am interested in forage for sheep and goats so I think they could easily keep it from doing too much harm.
Does anyone have a link to it's forage qualities? Also since it isn't known for being drought tolerant, wouldn't it just die if it is not being watered? ( I am in the great basin, high desert, everything here needs to be watered).

I have it in my garden, it is aggressive, however it is containable. So much of the "aggressiveness" in any plant depends on the climate, sun,shade etc. This year with all of our rain and cooler temps the Loosestrife seems to have been knocked on its heels. My containment consists of mowing it down if it gets into the grass or pulling it.
I like the way it looks!