Possible Culprits in the Case of Missing Gardenia Blossoms
Question: My ‘Mystery’ gardenia forms flower buds, but just as they mature to the point of opening, they drop. Can you suggest why they fall off?
--R.P., SIMI VALLEY
Answer: There are several possibilities, according to Kevin Naylor at Monrovia Nursery, a large wholesale grower:
* Nearly invisible bud mites. Other than using a 20X hand lens to spot them, the only clue is that the scales of the bud turn brown or black at the tips. Sevin will control the mites, but it is extremely toxic to bees and earthworms, so use it carefully. It also might result in an increase in spider mites. A rather radical but nonchemical control is to pick off and destroy all the buds and hope the next crop will be clean and pest-free.
* A deficiency of micronutrients, such as magnesium or manganese. Use a liquid fertilizer, such as Peter’s 20-20-20, that contains micronutrients, and drench the plant so some is taken in by the foliage as well as the roots.
* The soil might not be acidic enough. Gardenias like heat, sun and an acid soil. In winter--if the plant is small enough--dig it up, improve the soil with organic amendments and replant. Alkaline soils also tend to tie up micronutrients, so alkaline soils and soil pH are often linked.
* It is too hot or too cool, or the roots have been damaged from over-watering or root rot.
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Q: Can freesia bulbs be planted right away, or should I wait for a break in the heat?
--D.S., Northridge.
A: Freesias, like other bulbs that were originally native to South Africa’s cape region, are actually the first bulbs to plant. They take heat in stride and actually like a little baking in summer while they are dormant. Other cape bulbs include, babiana, homeria, ixia, sparaxis, tritonia and watsonia.
What you don’t want to do is keep these bulbs too wet, at least until they sprout. I try to find places in the garden that stay fairly dry in summer and fall--that get less water than areas like rose beds. Two such spots are at the edge of paths, or where sprinklers don’t reach. Another is in pots that I let go bone-dry in summer. Planting in pots or beside paths also puts the fragrant freesias where you might catch a delightful whiff while they are in spring bloom.
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Q: Help! Whiteflies--the giant variety--are everywhere in south Torrance. They are on coleus, common ivy, feverfew, begonias, hibiscus and even tall trees. Could you run another column of suggestions? We need help.
--G.B., TORRANCE
A: While there is still no silver-bullet cure, help is on the way, and in some areas has already arrived, in the form of three different parasitic micro-wasps. During the last few years, these wasps have been collected in Mexico and Texas, raised here by the millions, and then released in the coastal counties. They are already well-established in places such as Tustin and Long Beach so may actually be in your yard, according to John Kabashima at the University of California South Coast Research and Extension Center in Irvine.
Look at the oval whitefly pupae on the undersides of leaves and see if they haven’t turned quite yellowish, black or gray--signs they have been parasitized. “Parasitized” means there are very tiny wasp larvae living inside the whitefly pupae like some creature from the movie “Alien.” Unlike that alien, these parasitic larvae and wasps are completely harmless to anything much bigger than a whitefly, and they are stingless.
You can also check for parasites by looking for tiny emergence holes in the pupae, where the grown wasps have exited. You might need a hand lens to see them.
Kabashima says the wasps have really taken hold in Orange County, where Master Gardeners have helped disperse them, and that Los Angeles County should see improvement next year. At this time of year, the parasites--if you have them--should begin to catch up with the whiteflies and you should notice a difference.
People living right on the beach may still have problems, even after the wasps become established, he said, because the parasites don’t seem to do as well there. They are not at their best in deep shade, either.
Don’t expect all traces of the filament-spinning giant whitefly to vanish from your garden. There will always be some near the base of the plant, said Kabashima. The wasps always leave a few to eat later on so they never run out. “It would be like eating everything in the cupboard,” said Kabashima.
Down in San Diego County, where they have been releasing parasitic wasps for two years, extension center advisor Vincent Lazaneo cautions that the results are not necessarily dramatic. “Control can be spotty,” he said, “and you won’t see results overnight, even if you do everything right.” He said it may take a year or more before you see a real difference. In San Diego, it is still felt that a faster, more aggressive parasite is needed, similar to the one that almost immediately brought the Ash whitefly under control several years ago.
In the meantime, it’s important to stop using any kind of control other than a strong blast of plain water, or the parasites will also be killed. Ignore advice to spray with some kind of light paraffin oil or summer oil; these will also kill the parasites. Ditto for any kind of pesticide, including systemics. Whiteflies always recover faster from sprayings than their parasites, so you are soon in an ever-tightening spiral of more and more whiteflies and fewer and fewer parasites.
To control with plain water--which is the only university-recommended control and the one they feel works best--blast whitefly colonies with a strong spray aimed at the undersides of leaves. This will work if you are persistent. While the whitefly larvae cannot crawl back up once they are knocked down, other adults will lay new eggs (often inside those rings of waxy, white concentric circles) so you must blast them again, and again if necessary, until the parasites begin to help out.
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