A heavily planted tank is already cycled. Of course, people can still choose to follow a set of old procedure that is no longer required.
You really don't understand the definition of a cycle do you. All the plants do is mask the slow production of ammonia and other nitrogen based waste. This is only possible with a light bioload, and if for some reason you get a spike in ammonia the plants will not be able to react quick enough to take it out. Bacteria don't stop metabolizing these compounds. Plants stop when the lights go out. Plants don't cycle an aquarium.
Now if we're talking about the Walsted method, then thats different. But once again you need a low bioload or the plants/soil bacteria will not keep up with the waste production.
10G - Low Tech Planted [ Chocolate Neos, MTS, Tracked Nerite / Anubias Nana, Windelov Java Fern, Water Wisteria, Dwarf Sag ]29G
- Non Planted Native Tank [ Creek Chub, Yellowfin Shiners, MTS / Water Wisteria ]