How to transplant into the cardboard sections:
Call me lazy but I've been using cardboard or newspaper in gardens for at least 15 years. It's a quick and easy way to stop whatever was growing in the spot from taking over your new planting area, whether its grass, weeds, or other ground cover. It becomes a decomposing weed barrier that lasts long enough to kill everything beneath it but then, like magic, becomes part of the soil. It has an added benefit of being great food for earthworms, which are wonderful aerators in you garden, loosening the soil for your more desirable plants' roots. It's also a very green way to recycle cardboard and green goes hand in hand with gardening. Overlap your cardboard pieces a little. You know those weeds are persistent and will fight their way through any crack or crevice.But once you have that nice smooth cardboard weed barrier which you spread with rich compost, how do you plant into the bed? Ideally one would wait until everything is decaying beneath the layers but who has that kind of patience.
If you're like me you want an instant garden so you plant your perennials shortly after the cardboard is layed and the mulch is spread . I would not recommend planting on top of the cardboard. It's usually too shallow and tends to dry out very quickly. Allow the cardboard to soften from the dampness of the soil beneath it or speed the process a little by watering the area.