Describe the your request

As the title says, mechanical harvesters simply break the mushrooms instead of replanting them. And the fact that there is a chance of giant mushrooms to grow instead of colonies even when using Farmer's Delight makes it very tricky to automate the process.

Just wait for the mushrooms to grow into the farmer's delight mushroom colonies, and then you can turn on your harvester, it should automate just fine.