Cold? Where are you. In UK I would expect a tender perennial like Thunbergia alata to be killed by frost. Having said that, yesterday I saw a row of sweet peas in the lake district with no flowers on but plenty of green leaves. Since it hailed here this morning, howling gales and a power cut last night, I thought that was pretty unusual. The rest of the family gathering have gone out. I am staying in.
Assuming you're in the UK the answer will be that 'it's winter' . The one that is flowering is probably in a more sheltered spot, but it will stop flowering soon and both are likely to die if unprotected in the winter.
Thunbergia alata is a tender perennial so if you want to keep it for next year it will need to be kept in a warm conservatory or heated greenhouse. Most of us treat them as an annual and grow new ones from seed each year.
Thank you everyone for your replies & yes, we’re in the UK on the South coast. I will have a go at potting them & then put in our greenhouse which does get sunshine which, on most days, keeps it warm.
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Thunbergia alata is a tender perennial so if you want to keep it for next year it will need to be kept in a warm conservatory or heated greenhouse. Most of us treat them as an annual and grow new ones from seed each year.
More info here https://www.rhsplants.co.uk/plants/_/thunbergia-alata-suzie-orange-with-eye-suzie-series/classid.2000028594/