Looking at nature, most ecosystems "in the wild" don't have these problems that conventional gardeners do. In the wild, an increase of a certain pest would mean an increase in the predators of that pest! Rather than looking at individual problems, look at the larger system; can you make your garden mimic a natural ecosystem? How are plants spaced? In nature, plants are crammed in everywhere, with no bare spots. How many different species are there in a given space? In a space the size of a small garden, there could be hundreds. What other living things have access to the space: animals including reptiles, birds, mammals, amphibians; insects, plant-eating, pollinating, and predatory; invertebrates like slugs or worms; and so on? Systems which have a huge amount of diversity are set up to succeed.
Getting to the point of where your garden is sustainable takes time. I've been applying
permaculture practices to my garden for two years now, and this second year has been much more of a success than the first year, and even more so than in the past when I was simply organic. Some of the things I've been doing to mimic nature:
1) No weeding and no compost pile. Chop and drop only.
2) Sowing lots of different species of seeds in all areas, including
natives, edibles and ornamentals, and not in rows, but just broadcasting everywhere.
3) Allowing every kind of insect and invertebrate access to my garden, including "pests", and taking note of how they affect my plants, to help with future gardening plans.
4) Allowing some parts of the property to be just wild, to provide habitat for small predators, which in my area are frogs, toads, hedgehogs, song thrushes, blackbirds, etc; this ties in with #3 above, as the more pests there are, the more the predators will want to move in. Have left piles of sticks on the margins of the property, or piles of leaves, and left a few patches of lush, overgrown weeds dotted about.
5) Planting support species; in my case I planted comfrey, and sowed crimson clover and alfalfa among the other edibles. Other support species are the weeds that self seed such as dandelion and
nettle.
And some of my observations:
1) The cabbage white moths had a very difficult time finding my cabbages and other cruciferae, as they were hiding amongst a huge jumble of other plants. In previous years, the caterpillars have completely defoliated whole broccoli and cabbage crops in just weeks. No discernable damage this year. I watched them fluttering around the garden, obviously knowing the cabbages were there somewhere, but not being able to find them!
2) Same for the cabbage
root fly; did not seem to find the turnips this year, unlike in past years.
3) And again, no real problems with aphids; I've seen the sparrows and finches perching on the roses and stripping them off.
4) Some slug and snail damage to cabbages, particularly later sowed seedlings. May need to time my cabbage sowings to early parts of the year, rather than later.
5) Seen lots of birds in the garden, one hedgehog and a couple of frogs this year. Would like to encourage more frogs and toads, so thinking about a tiny
pond or other
water feature.
6) In some edibles, I have seen a big increase in yield, such as turnips, runner beans, cabbage. In other edibles, not so much of a difference from last year: broccoli, onions, potatoes; though I've been feeding the soil using chop and drop and with organic mulch (from an outside source), I think I could really ramp up production after using these methods for a few more years.