C. Letellier wrote:Almost all herbs, almost anything that blooms. Avoid the ones used as insect repellents and you are good mostly. The next question is what else it does for you? Does it fix nitrogen? Does it have market value in your area? Does it improve your diet? Not saying the other things are required but if your space is small they should be.
Jamie Chevalier wrote:I've been working on the subject of beneficial insects for some years now, and there are several things that stand out in my mind as important:
-A variety of flowers (Xerces Society says that in tests, the largest number and variety of beneficials was achieved with 20+ species of flowers in bloom.)
-Flowers all season, from very early spring (ie, still winter) to late fall.
-As many natives as possible. There are many native pollinators and predator insects that have co-evolved with specific plants, and can't do without them.
-Almost all herbs have good flowers for beneficials. Herbs are seldom bred for human-pleasing flowers and are thus still tailored to the needs of wild insects.
-Habitat should not be overlooked: piles of sticks to attract ground beetles, perennials for overwintering, etc.
-A variety of flower shapes, colors, sizes, being sure to emphasize singles over doubles, and to include lots of small and inconspicuous flowers like alyssum, orach, cilantro, amaranth, chervil, etc. as well as trumpet and foxglove shapes. Quail Seeds carries several seed collections specifically for attracting beneficials, tailored for the season and planting regime (annual, perennial, ground cover, decorative border, etc.)
-Some pests are always around, while some have a short--but potentially devastating--window. During those times, plants that are normally great for attracting beneficials may prove to be liabilities. For example, during late June/early July, brassicas host so many flea beetles and such destructive hordes of harlequin bugs in my area that I ban them from my garden until late July. That way, the coast is clear when I make large brassica plantings for fall. While arugula, kale, mustard, and even tiny weeds like shepherds' purse are normally wonderful attractors of beneficial tachnids, bees, syrphids, etc, they are not worth having around during the harlequin-bug window.
--It is obviously impossible to micromanage every interaction, and it's generally better to just have a bunch of stuff. HOWEVER, if you have one or two pests that have been a real problem, find out as much as you can about what attracts them, and what attracts their enemies. For example, if thrips are a big problem for you (and I have had them reduce tomatoes to a dry skeleton) you should know that the clover you planted for the bees attracts and shelters thrips, leading to worse damage than if it were bare ground. (There are a couple of research papers that studied this, available online.) On the other hand, alyssum as a flowering groundcover attracts the main predator on thrips, as well as bees and lots of other beneficials.
While it does sound strange, leaving aphids alone can in fact be a strong strategy for attracting and keeping beneficials. You won't have them on hand in large numbers if there are no prey for them, after all. Once I noticed that my poppies were getting a bad outbreak of those big fat black aphids that appear in early spring. Curious, I left them alone and checked them every day. Within a couple of days, wasps had found the poppies with aphids. Within another 3 days, the aphids were gone, completely vacuumed up by paper wasps. While the most numerous predatory wasps are small (down to gnat size) and stingless, it is also true that bigger more fear-inspiring wasps are formidable predators. (Generally speaking, the ground-nesting wasps are more aggressive than I can deal with in and around frequented areas, but tree-nesters are better, and solitary mud wasps downright tame.)
That said, aphids (whiteflies, thrips) are different from squash bugs. Large bugs that target and ruin the fruit are very different from small sucking insects that very gradually sap the plants strength. Diatom dust on the squash stems works well for me, combined with searching for and destroying eggs. I notice they generally crawl around the plant rather than flying, so the stems are their highway. I have also had success with an understory crop of radishes beneath and around the squash, to disguise the distinctive squash smell.