Thank you. The first time I ever wormed a flock, two years after they hatched, was when I saw a roundworm in one rooster's poop. So, everyone was wormed. I think I used Safeguard paste, can't recall exactly. Then, they were pretty much wormed once a year after that, unless I felt a specific need to worm one group of birds an extra time.
Natural wormers are only mild preventatives and will not kill all worms or the tougher worms like capillaria or tapeworms. Curcurbit in pumpkin seeds is one of those, but it cannot be depended on to worm reliably. Garlic doesn't worm birds. It may be an immune system booster, but given in excess can cause anemia, I've read. DE does not worm birds because it loses cutting power when wet, which it is inside a chicken. And I use it in my coops under the roosts but see all sorts of worms in my compost pile, a warm wet environment with lots of DE from the piled-up shavings.
Since worms can kill if they completely overrun the chicken's system, they really should be wormed about once a year, IMO, using the safest, all-inclusive wormer which is Valbazen. Valbazen kills all poultry worms and starves them out over a 3 day period so as to not clog the system with dead worms. Invermectin has become ineffective for many people, though the pour-on is easy to use and cheap. That used to be my choice until a bird was necropsied just a couple months after worming and had both roundworms and capillaria (not the cause of death, just an adjunct to her internal infection). I understand you're supposed to rotate wormers, but not sure it would help if the one you rotate with an ineffective wormer.
Penned birds need worming more than birds who are out on lush forage, free-ranging regularly. Since mine have had less free range time and more time inside the barn, I've had to worm twice a year. An otherwise healthy bird can handle a mild worm load without it affecting its health adversely, but best to not allow them to build up to overload.
Natural is all well and good...until it doesn't work. Since worms are a drag on the system, seems a little nuts to hold onto a natural principle that isn't working and sacrifice the health of the animal.