Can’t water? Bulbs unlikely to mind
To those of you who are forbidden to use sprinklers or hoses through Sept. 20 due to water pipeline repairs, don't panic. Established trees and shrubs, as well as herbaceous perennials such as lily-of-theNile (Agapanthus), daylily (Hemerocallis), canna and, especially, irises (many of which originate in a climate similar to ours), will not suffer significant, if any, damage due to lack of water over such a short period. New plants, especially anything planted from a container smaller than a 5-gallon size, are likely to suffer, so put some sort of shade cloth or mesh tarp, available at home improvement centers, over them during the day. A 4-inch layer of mulch, whether wood chips from a tree trimmer, cedar mulch by the bag or shredded newspapers, will minimize water loss from the soil surface.
Herbaceous perennials are plants that grow from bulbs, tubers, corms or rhizomes. These plants are especially resilient, so even if their foliage should shrivel for lack of water, their underground organs that store life-sustaining carbohydrate will allow them to bounce back once they are watered again. And many, such as cyclamen, go dormant this time of year and would be killed if they were watered. So for color in the garden, it's wise in these droughty times to plant herbaceous perennials. Relying exclusively on them for garden color, it is possible to have a kaleidoscopic collection of flowers throughout the year. The suitability of herbaceous perennial blooms for cut flower arrangements is a bonus.
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“You and others have been encouraging gardeners to plant narrow leaf milkweed to attract monarch butterflies. This last spring, I heeded this call for the first time and now have several large, heathy-looking milkweed plants in pots. But … for the last two weeks I have had an infestation of oleander aphids. What do you recommend (besides squishing them one-by-one)? Or doing a temporary rental from Rent-AMantis? I don't want to do anything that might harm monarch eggs or baby butterflies-to-be. Please respond soon, before the aphids gobble up all of the plants.”
First, the good news. Even though the intense clustering of aphids on milkweed may look hideous and threatening, aphids generally do not perturb monarchs. Moreover, it is unusual that aphids actually damage indigenous milkweed plants. Keep in mind that when California native milkweeds go dormant and effectively disappear
for the winter, their pestiferous aphid companions disappear along with them.
The easiest way to dispatch oleander aphids — bright orange with black legs — is to blast them with a strong jet of water. Don't worry about knocking off monarch eggs since they are more strongly attached to their milkweed host than the offending aphids. Alternatively, as you suggest, you can always rub aphids off of milkweed with your thumb and forefinger.
You can spray and kill the aphids with neem oil (made from seeds of a tropical tree), but you must wash down the milkweed with water immediately afterward since monarch caterpillars would be killed
if they chomped on stems or leaves coated with neem.
Detergent sprays are commonly recommended for aphid control, the simplest concoction being 1 tablespoon of dish soap dissolved in a quart of water. However, according to Karen Oberhauser of the University of Minnesota, who has studied aphids, monarchs and milkweeds for decades, “Detergent treatments will kill any live insects on aphid-infested plants, including monarch eggs, monarch larvae, and aphid predators like syrphid fly larvae, ladybug larvae, and lacewing larvae. (Note: By the same token, you do not want to release large populations of aphid predators because they are inclined to munch on monarch eggs as well as aphids.) There is really no good way to kill aphids without killing everything else, except by trying to lower the population by carefully killing them by hand.”
Aphids are fascinating insects, and oleander aphids all the more so. They are both viviparous and parthenogenetic. “Viviparous” means they give birth to live young, just like mammals. The difference is these offspring, also known as nymphs, are clones of the mother. They will molt four times over the course of their lifetime, which lasts 25 days, and will give birth to as many as 12 aphids in a single day.
The fact that oleander aphids are parthenogenetic means mating is not needed for reproduction and, in fact, no male oleander aphids have ever been found. If a milkweed plant is totally overcome with aphids, some of them will sprout wings in order to fly to another plant and continue reproducing there.
What appear to be white flakes are common on an aphid-infested plant. These are the skins aphids shed when molting. Dead aphids — puffed up or bloated — are brown or black and are frequently spotted when examining an aphid-infested plant. These dead aphids have been cannibalized by parasitic wasp larvae. Tiny wasps, no bigger than a pencil tip, pierce the bodies of aphids with an ovipositor through which an egg is passed. As the wasp larva hatches from the egg, it consumes the inside of its aphid host before pupating and emerging as an adult.
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The Southern California Begonia Society will present a two-day show and sale at Sherman Gardens from 10:30 a.m.-4 p.m. Sept. 17-18. A large selection of begonias not typically found in local nurseries will be available for purchase. Experts will be on hand to answer your questions and enhance your begonia education. Sherman Gardens, home to over 130 begonia varieties, is at 2647 E. Pacific Coast Highway in Corona del Mar. Admission is $5 (for members, it's free) and includes access to the begonia show.
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Note: I wrote in a recent column that common yarrow (Achillea millefolium) is a nonnative plant that attracts monarch butterflies. Well, this species does attract monarchs, but it is, in fact, native to California, being found in every county except two. I want to thank Gordon Lemke for drawing my attention to this fact.