Hello Lenette, one of the most common varieties of Longan is Kohala and they are very vertical in their growth habit. A 6ft tall tree should ideally be 6ft wide in my opinion. I've seen many longan trees that are just way too tall. Do you plan on keeping your tree potted? If you are going to keep it potted, a good draining soil is recommended but since you only water when it dries out, its not as important. You should actually check the soil several inches deep, maybe ~6-8 inches deep to determine when to water. Sometimes the surface of the soil can dry out but the interrior can still be really moist if you do not have a good draing soil mix.

Since you are keeping your Longan in a greenhouse with a heater, it may not fruit this year because they like a little cold and drought to initiate flowering.

I treat my Longan the same as I treat my Lychees. Lycheesonline.com has lots of great info on growing Lychees which you can use to grow Longan. Good luck and let us know how your Longan does!
Simon

Hi simon_grow. Thank you so much for your reply it is greatly appreciated! I am going to keep it potted for now since its possible that we could get temps down into the low 20s a few times during the winters although it has not gotten that cold yet this year (seems to be an odd winter here). I will repot it in the spring. Good reminder about checking deeper for moisture! These large pots can be trickier.

I don't think my tree is 6ft wide it is probably more like 3 1/2ft wide. I guess I have some work to do lol.

How much cold should it get in the winter to flower? I don't wanna kill it but could leave it out on the nights above freezing which is most of the time...

I read somewhere that Lychees can be fertilized using the slow release fertilizer in the spring. So is it same for Longans?