Once upon a time there were three small healthy gardens.

The first and oldest garden was once very carefully weeded by its owner.   A large group of plants, big and small, dense and viney, woody and grassy, all interacted to each other's benefit.  Then the owner decided that weeding was too time-consuming and stopped doing it.  Instead, on the idea that ignoring the weeds would make them vanish, the plants were given eyeshades so they wouldn't see the weeds that were slowly overwhelming them, choking off their beneficial interactions with each other.  That being seen as not helping matters, the gardener announced that all plants therein would henceforth pay for the privilege of growing.  This drove out all the weeds, but it also drove out many of the best plants.  This scheme, too, was abandoned, and the garden was left to the weeds.

Like the owner of the first, the owner of the second garden decided that weeding it was too much effort and didn't provide any direct profit, so the garden was allowed to "self-weed" on the idea that the remedy for bad plants wasn't to remove bad plants, but provide more good plants.   Unfortunately, the bad plants were organized like aspens, with their roots connecting them and allowing for shared peril and plenty; when one bad plant was under attack, its fellow bad plants came to its aid, eventually driving out the good plants - many of which were uprooted by the gardener as they were mistaken for bad plants.  This garden grew and grew, but its character had changed, and not for the better; no more would its creator be able to control it, save for plowing it all under.

The owner of the third, smallest garden used to be a stickler for weeding, which made the small garden a surprisingly good one for its size, with far more really good plants than most people thought possible in a garden so small.  Then a cash flow crunch hit, and this garden's owner decided to forsake actual weeding for self-weeding as well.  Just as with the first and second gardens, it wasn't long before the weeds had overrun this garden, stifling and driving out all the good plants; as with the second garden, the weeds had aspen-like connections, except theirs were even stronger.  They wrested all control from the owner, leaving the owner without the ability to even exert the mildest influence on the garden and its plants.

The lesson: If you want a garden where plants can interact productively and enjoyably, you have to weed it religiously and not abdicate the responsibility, or your garden will soon be awash in weeds and bereft of all but the most basic weed-dictated interactions.