Keep a Cineraria Plant moist but never soggy. Always allow the top inch or two of soil in a Cineraria Plantto dry out before watering. Cineraria Plants can sit in the excess water for 15 minutes then be sure to empty the saucer. The more blooms a Cineraria Plant has, the more water it needs. Note it is not a vegetable. The Dusty miller version is a common ornamental that is relatively care free. It is nota big plant.so your 20 inch pot should be more than adequate. https://plants.thegrowingplace.com/12120014/Plant/14475/Silver_Dust_Dusty_Miller/

I was not familiar with that common name so had to look it up :-) Apparently sliverdust is a just another name for a form of dusty miller, Jacobaea maritima, aka senecio. Have used it as a participant in a mixed container planting as it doesn't have much presence as a stand-alone container subject. Only gets to be about 12"x12" so a 20" container more than adequate. Very easy to grow, needing full sun and minimal water. Do not keep soil media too wet.

ps. Jacobaea is NOT the same as Cineraria and requires significantly different growing conditions. Be sure to accurately ID what you are growing first :-)

Thanks Guys

Just Realized That I Missed The Word Squash Of The Title After Reading Your Replies.....

That'll Teach Me NOT To Post When Tired!

But I DO Like As Well Cineraria Plants As Well So Will Probably Get One When I See One As I Now Have a Patio To Myself.....

LOL!! Well, that makes a difference!! 😊 A winter squash plant should grow perfectly in a 20" container. But it will extend well over the sides for some distance so be sure to allow for that spread. And you will need to be careful about watering, not allowing the potting mix to dry excessively.