Hello Ducky, unfortunately this is a bug with the vanilla expanded framework. A workaround would be available, but it can be exploited. If you are interested, I can explain how to fix the bug. Whether you exploit it then is up to you.

that would be really helpful, i would really like to use silk, since its used in a few things

*) Navigate to: Steam\steamapps\workshop\content\294100\2553700067\1.4\Defs\ThingDefs_Plants
*) Open "Plants_Cultivated_Farm" with an text editor of your choice
*) Search for "DankPyon_Tree_Mulberry"
*) Search for "harvestAfterGrowth" (which should be 22 lines below the line, that hold "DankPyon_Tree_Mulberry")
*) Change the value from 0.30 to 0.41
*) Save the file
*) Enjoy

This not only allows you to harvest silkworms, but also to manually harvest the tree after it has been harvested. This way you can harvest the tree indefinitely. Absuing this mechanic is up to you though ^^.
Without set the tree for manual harvest, everything should work fine though, at least according to my last play-through.

okay thank you so much!

It worked!
Now I can finally build some royal beds for customers.

Have they fixed the bug?

Yes, the bug is fixed. You both get mulberries and silk worms when harvesting mulberry trees.