cracks in rootstock after freeze

[quinoah]

hi!

unfortunately some of my rootstocks have cracks...
I think this is not due to general deep temperatures.  over winter my citrus were covered by some kind of greenhouse, after winter everything was green and fine. it got warm inside, but not too much, plants seemed to break dormancy(no new shoots or buds visible).
after uncovering the citrus it got pretty cold again for two nights 
the rootstocks are swingle, can cracks heal and be able to feed the grafted variety? the grafted varieties have no cracks, but major twig damage, they could be still alive.

thanks!

[pagnr]

Some photos would help to get a better idea of the problem.

[quinoah]

I'll make photos when I'm visiting my trees again

[tedburn]

I know this problem also, citrus are in good shape when remooving protection fleece end of february or march and then deeper nightfrosts and daysun and higher day temperatures then lead to bark cracks. Some of them heal, some lead to infected and dying twigs or
plant. This means to protect against daysun while nigt freezes below -3 or -4 ° C arises and to kerp the plant protected and dormant.