IMO, the jump from a 4" pot to 2 gallon is too big. As pot size increases, the *volume of soil* in the pot increases by a factor of 4. All tht soil is empty of roots, so it never dries out. As you water, a lot of wet sludge builds up in the bottom of the pot, rotting the roots. Rotten roots = dying or dead plant.

Go up one size pot at a repotting. So 4", go to a 6" pot. Jasmines also benefit from a clay pot, which dries out faster.

I would take them out of the 2 gallon, and if there are any live roots left, report to the smallest size that just fits the roots. By now, even a 4" could be too big, so be consrevative.

I think what you said is right. 4" pot plant should not go in 2 gallons pot. Although I am very careful with my Potting medium. Lots of Perlite, Moss, Humus and very little soil. One plant I think I murdered all leaves are dry. I pulled it up, Lots of root but soaking wet. I re-potted it in 4" pot I don't think it is going to work. Also I made the problem double the pots had poor drainage. For the other three which still have some life in it I opened lots of drainage holes and since it warmed good today I left them in the Garden soil hopefully the ground will help drain them up. I learned my lessons. I just ordered 3 plants from Almost Eden the plants were described as "Grand Duke of Tuscany Jasmine Sambac Flor pleno" They come in 4" pots I will make sure to use small pots with good drainage holes. If they grow out the small pot I can report them later. I am not going to make the same mistake again and Thank you for your information.
Abe

Abe, you will love the Grand Duke from Almost Eden. It is very fragrant, and quite vigorous.

With spring and summer coming on, your plant will put on lots of growth as soon as the nights warm up. If you repot one size up (but no bigger) each time the roots fill up the pot, you will have a really nice size plant by the end of summer.

About your sickly jasmines-- winter is very hard on jasmines. They like lots of sun and warmth. Mine always end the winter looking not too good, but put on bursts of growth as the sun gets stronger. My neighbor, who has some 20 year old jasmines also. But a too-big pot is almost a death sentence, especially in winter.

Starting with strong new ipants this time of year, you will be greatly rewarded with big good plants growing and giving you wonderful fragrant blooms.

Good luck!

I wonder if Duke of Tuscany is just one season pony orcomes back next year.

You can't grow the Grand Duke in the ground in Zone 7. In a pot, it is perennial, puts out new growth every spring. Lots of people cut back for winter to protect the plant from bugs and other winter woes, but as soon as the nights warm up in spring, it will bust out all over with new growth.

If you are lucky, it will be a forever pony. My neighbor has huge jasmines with trunks as big as my wrists that she's had for 20 years. Every year she takes them in for winter. Eery spring she puts out the huge pots full of brown sticks. And then, whoosh! One morning they are all greened out.