Kadomatsu are decorations made mostly from bamboo and pine.
They are put up after Christmas and until January 7th.
You put a pair outside the entrance way.
門松/Kadomatsu literally means “gate pine”.
They welcome ancestral spirits to your home or business and are the temporary houses for the spirits.
(So, definitely don’t put your umbrella in them)
On the 15th of January (or the 19th in some cases) they are burned to release the spirits.