We bought some Federation Daisies yesterday, and when I pulled the plant out of it's pot today I found it's fully root walled. This is my first flower plant ever so forgive my ignorance but should these roots be trimmed or just placed in a bigger container of soil? I'm surprised they would be sold needing immediate attention like this but I'm sure I was told that roots need trimming at this stage.
If the plant roots are potbound gently work them loose some then plant into bigger pot. If one trims the roots it will shock the plant a lot more and possibly set it way back or cause it to fail. If the roots are trimmed the top also needs to be trimmed and again this may not be good for the plant.
The new pot, a good next size up is two inches larger diameter. This gives growing room and prevents the edge soil from going 'sour' (building up salts and such) because of lack of roots in that zone. At end of season it is not unusual for bedding plants and other potted plants to be 'too big for their britches' with overtall top growth and very root bound. This sounds like your daisies.
I agree with Deb Rebel. However I will ask a bit more but likely she is on point and what I speak now is just for understanding.
How does the top side of the plant look?
If it is healthy looking, as Deb stated, I would not worry about it and just loosen up the roots so they dangle a bit and transplant normally.
If the plant looks unhealthy you can trim some roots but only a wee bit, perhaps a quarter inch of roots if that. (of course any roots that are diseased or rotted but dont think that is the case here).
I like to water in with a soluble/liquid fish fertilizer mix when transplanting but is very important when and if you have to trim roots. For those into natural farming, some OHN and some FPJ would be spot on as well. When transplanting after trimming roots I like to use a good mushroomcompost to help address any dead roots as it will help decompose them.
For most, it is kind of rare to need to trim roots but many think they need to do. Being root bound is not so bad once the plant has room to grow, just untangle a bit but dont get too helpful as root hairs can be easily harmed.
Expect a minute or two for the plant to recover and it may look sad while it does but is normal. Do not over fertilize at this stage as the plant cannot uptake normally, 1/4 to 1/2 dose of what you would normally do should keep you in safe area.
You will do well!
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Potted plants that are going to remain in a container don't need much root care, just a little squish of the root ball as Deb mentioned does just fine for repotting in a larger container.
I think most of the "cut the roots" confusion might be coming from Bonsai practices where you do trim the roots (these are trees though, not flowers) and repot in the same container.
The root trimming is what keeps the bonsai from growing to full size.
If you were planting from a container into the ground, then you need to tease out the roots prior to planting then use a good root stimulant to water in after planting in the ground.