I've filled a plastic bag with styrofoam "peanuts" (any light weight material would do - empty plastic water bottles, soda cans) and put that at the bottom to fill up some space. Most annuals don't need great depths of soil and with my method there is still proper drainage.

If you live in an area with a long growing season, you won't want too shallow of a root/soil zone. I'm always amazed at the massive root system after 6 or 7 months.

My favorite method is to cut the legs of pantyhose into two sections and tie one end on each, fill with packing peanuts then tie off the other end. Mesh onion bags work great, too.

There's no reason to fill the whole container with potting medium, if it's as big as you say. Just be confident that there's ample room for growth down below or there won't be as much on top.

the easy way.. is to do pot in pot.. and fill the excess with whatever you want ...

filling it all with media.. would not be cost efficient..

some peeps just find an empty pot in the recycle pile at the nursery.. and invert it in the decorative pot.. and set the plant pot on top ...

a pic of your pot.. might get better ideas ...

ken

"the easy way.. is to do pot in pot.. and fill the excess with whatever you want ...

filling it all with media.. would not be cost efficient..

some peeps just find an empty pot in the recycle pile at the nursery.. and invert it in the decorative pot.. and set the plant pot on top ..."

I have a neighbor who did this. She has a huge pot in her yard, at least three feet tall and very large in diameter. I often wondered how much soil did it take to fill it.

While at her house one day, I took a look and noticed she simply placed a more shallow pot of similar diameter inside it. I didn't bother to ask what was supporting the smaller pot underneath, but it really doesn't matter.

I do the same. Use a cheap plastic pot inside the bigger pot. It can't be seen from the outside and if you have several you can swap the displays easily rather than having to dig out and refill the planter in situ. Here's an example. The Fuchsia is actually growing in a plastic pot like the one behind the terra cotta pot. It sits inside the larger pot. (The plant is a bit scruffy because the photo was taken in November.)

dont know where you are ... but up here in ground freeze great white north ...

very fancy pots need to be emptied and dried in fall .. and then stored for winter...

else mother nature can shatter them ... with the freeze/thaw cycles ....

and that is another reason to use pot in pot ...

if you are in said area.. we can discuss what kind of pots.. and how to do it.. etc.. preferably in a new post with a proper title ...

ken