Theoretically, what you did sounds fine. Without pics, this discussion can only be theoretical, not specific feedback about your specific plant.

"I loosed up the root ball before putting it in the new planter and potting medium."

Doing this always worried me and I rarely do it unless very small plants are totally packing their roots in the old growing pot. Any air left inbetween the roots is a killer. I might spread out the edges a bit, but never loosen the core.

Otherwise, I haven't any thing else to recommend.

Thanks. What do you mean by 'any air left in between the roots'? Why would that be a 'killer'? And, so long as I added plenty of soil to the new planter, watered in between, let the water get absorbed...the overall amount of soil fell down further...I add more potting soil....pressed down...watered again...added more soil and so on, until soil was 'solid' in the planter, and then gently pressed soil all around the plant crown...the stems...at the soil line, to ensure plant was firmly in there...no air pockets...

So could there still be 'air in between the roots'? And even if there were, could that have cause the plant to deteriorate to quickly...like with a day or two after repotting?

Thank you.

We need more information and, preferably, pictures. A plug is usually so small that the roots need little grooming. We don't know where you live but for many of us it is late in the year to be planting basil. Are you growing indoors or out? Basil is normally unfussy.

Yes, pictures can help.

What I mean is: When you spread out the roots from a root-mass, and maybe wash and trim away any dead roots, there is no soil left inside the root-mass. When you add soil back in you have to make sure that you get lots of soil packed back inbetween the loosened root-mass or there will be air gaps. Roots need the soil right up next to them or they die.... they can't "breathe" air.

In your case, if there wasn't enough soil inside the root-mass the plant would die quickly. Which is why I never undo the root-mass, only very gently spread-out some of the most exterior roots.... amd then only IF the plants look root-bound,

Hope this helps. Still don't know what other cause there could be for your plants to die so quickly..... unless it's bad water, ei: heavily chlorinated. ???

Thanks...yeah...I can't imagine it's a case of air around the roots. I mean, this is how I repot all my plants and...I think between my constantly adding additional potting medium during the repotting process...then watering...letting the water soak through...which in turn makes the soil compact down more....then adding more potting medium...watering yet again...letting the soil compact more still....pressing down on all the soil to get out air pockets...adding still more potting medium...watering...and so on...I think it's fair to say that the root ball gets filled in with the soil/ammendments.

And I don't think it's the water...same water I always use. ;-)

Anyway, I've since cut back all the stems where it was clear that the leaves were beyond any possible 'perking up' and...while the plant now looks a bit sorry (bare), the leaves that remain DO seem to have perked up a bit. And I see minute signs of new leaf growth on the otherwise barren other stems.

So there may still be hope. ;-)

FIngers crossed! 🤞🏻

Compacting and pressing are the top 2 things I try to avoid doing when repotting plants. For the first 4-6 weeks, I water especially gently to prevent compacting the soil. From what I've read so far, root damage from the compacting seems the most likely cause of the damage.

Maybe I misses something here but I don't believe we know if this basil is being grown inside or outside. And if outside, where are you? It matters., Basil is easy in containers normally, but it's a tropical plant, unlike the majority of other common herbs that are essentially Mediterranean. Basil likes it warm and is not as finicky regarding high humidity, plants like lavender and rosemary really resent prolonged, high humidity. If you are growing it outside, what temperatures does it have? Basil is not cold hardy at all. On the positive side, it is easer to grow inside than many of the typically Mediterranean herbs.

Thanks all. I compact/press the soil when repotting, with all my plants, and it's never been problematic. I'm not saying I press down like crazy, but enough to get rid of air pockets and to ensure that crown of plant and stems are well supported by the immediate surrounding soil.

Plant was growing outddoors (Zone 6b) right up until I repotted it a week ago. I now plan to keep it indoors by a sunny window. As mentioned above, since repotting, I did cut back a lot of the plant, especially where it was apparent that the current growth was beyond recovery (super limp leaves). What remains of the plant is now looking better...the leaves have perked up. So I remain hopeful. ;-)