“We’ve lived in our house for 35 years. For the first 20 years, we planted white petunias up the front walkway to our house from about May to September. Beautiful in the summer. About 10 years ago, they started to die soon after they were planted. We had our gardener change the soil (one year), change the watering frequency, and other things so that we could continue to enjoy the pathway of white during the heat of summer. Nothing has worked. We even substituted white vincas and they don’t work either. Everything dies. My gardener swears that it is not the soil (he has also enriched it). I want to line the front walkway with white flowers during the summer. They look cool and restful during the heat. I am wondering if you have another white flower recommendation.” – Mary Bawden, Redlands
Unfortunately, soil enrichment or even replacement may not eliminate pathogenic soil fungi that can live to a depth of six feet or more. You might consider removing the soil where you plant petunias and sinking planter boxes into the ground in that area. Then fill the planter boxes with bagged planting mix and you can be assured that no soil fungus will waylay your petunias. This is one of the reasons that some backyard vegetable growers raise their crops in large planter boxes. They bring in designer soil, add fertilizer and are rewarded with fast-growing plants that produce abundantly.
If you want to stay with the existing soil, you might consider four annuals with white flowers that bloom at the same time as petunias, grow to about the same height, and have demonstrated resistance to Phytophthora, the most common soil fungus. One of these is sweet alyssum (Lobularia maritima). It sends out foamy waves of flowers classically in white but also in purple and magenta rose. Profusion zinnia, Angelonia, and moss rose (Portulaca grandiflora) bloom in a variety of colors, including white.
If you decided to forego annuals for a low-growing perennial you might want to choose white trailing lantana, which flowers on and off throughout the year. If you desired something shrubbier, white crown of thorns would be an excellent choice since its white bracts are visible not only in summer but all year long. Roses are resistant to Phytophthora so you could also plant low-growing types such as white miniatures or white polyanthas, both of which do not top two feet in height. Although flower carpet roses are ostensibly a ground cover and are available in white, they will grow up to four feet tall unchecked so you would need to prune regularly to keep them low to the ground.
Your failure with vinca after planting petunias is not surprising since vinca is also susceptible to Phytophthora infection. Not only are petunia and vinca killed by soil-born Phytophthora but there is an airborne Phytophthora type that is also lethal to them, infecting leaves and stems. Other annuals and bedding plants susceptible to Phytophthora that you would not want to plant in that area include pansy, snapdragon, begonia, calendula, stock, dianthus, and verbena.
Joan Gibson emailed about a tomato problem as follows:
“I have planted tomatoes at my garden in the Sepulveda Garden Center in Encino for many years. However, for the last two, they have been attacked by what I have been told are spider mites. I have sprayed this year with Neem oil and had to stop with the heat spell. My older tomato plants have turned brown after producing fruit (Early Girl variety) and the new plants also have withered and turned brown. What might the cause be? Is there something to do over the winter to kill whatever is attacking them?”
As in the case of petunia – which incidentally is a tomato relative, both being members of the nightshade family – planting of tomatoes in the same location year after year is bound to eventually lead to disease or pest infestation. Mites, which are arachnids and thus distant cousins to spiders and ticks, are attracted to dust and feed mostly on the undersides of leaves so it is a good idea to regularly direct a strong jet of water to this area of concern if you are in a dusty location. The Sepulveda Garden Center, which fronts the Ventura Freeway, is likely to get some dust and other particulate matter stirred up by the thousands of cars that pass by every day.
Gibson mentions that she stopped spraying during the heatwave even though she was using Neem, an organic product derived from a tropical tree. This was a wise decision since pesticides sprayed in hot weather can volatilize or turn to a gas that burns plants. As a general rule, it is advisable to spray in the early morning or early evening and never when the temperature exceeds 80 degrees and the relative humidity is less than 40%.
Prior to the onset of winter, spider mites lay eggs and hibernate in plant debris or in tree bark crevices. You will never get 100% control of spider mites once you have them but you can minimize their presence in your garden.
The tomato red spider mite which is plaguing Gibson’s plants may be controlled non-chemically by predatory mites. Rincon-Vitova insectary in Ventura is a main source for beneficial insects of all kinds, including predatory mites that have been found to control tomato red spider mite. The insectary recommends the release of a combination of predators, such as predatory mites together with green lacewings since “using more than one predator adds diversity and stability to your biocontrol program.”
To be effective, however, beneficial insects of any kind are best released as soon as a pest is identified. Once a serious infestation has occurred, it will be much more difficult to bring the problematic pest under control. Most common insect pests have munching or parasitizing foes that can be ordered at rinconvitova.com. If you do plan on releasing predatory mites, do it when the temperatures are above 45 degrees since mites stop growing and mating in cooler temperatures.
In rotating Gibson’s tomato patch with another crop, it would not be advisable to plant other nightshades such as eggplant, potato, and bell or chili peppers, which are also attractive to tomato red spider mites. Additional plants that host the tomato red spider mite include beans, roses, and citrus. Care should also be taken to uproot any black nightshade (Solanum nigrum) plants, favorite hosts of tomato red spider mites, that are growing in the vicinity. There has been a proliferation of black nightshade in recent years and you can see it popping up everywhere. Black nightshade is easy to identify by its white star-shaped flowers with thick clusters of bright yellow anthers in the center and purple-black fruit. Some people call it a weed while others consume its sweet berries, which must be done with caution since some black nightshade strains are toxic.
Classic crop rotation is a four-year phenomenon where crops from different botanical families alternate in a given area of a vegetable plot. However, growing cover crops, particularly legumes such as clover, can do much to recondition and enrich soil between vegetable crops, especially following heavy feeders like tomatoes. White and crimson clover are recommended as cover crops to plant this time of year. They are also called green manure since they may be turned under and mixed into the earth prior to planting the area once again. After your green manure crop is turned under, make sure to wait six weeks until its decomposition is complete before planting your vegetable of choice.
Tip of the Week: Just the other day I noticed a large branch from a liquidambar tree lying on the ground. It had broken off and fallen during the heatwave. I researched the phenomenon and learned that this is a frequent occurrence this time of year. The phenomenon even has a name: summer limb drop. I know that eucalyptus trees, due to their brittle wood, are notorious for dropping branches in almost any season and have warned people over the years never to park under a eucalyptus for that reason. It turns out that ash, oak, liquidambar, and pear are also known for dropping branches, especially in the summer. The phenomenon is not completely understood and both drought stress that causes a weakening in the branch and an overabundance of water that adds weight to the branch are used to explain it. Perhaps a branch is initially weakened by drought and then, when water is available, the tree overcompensates by pulling up more water than the weakened branch can manage. In any event, the branches that fall are consistently horizontal in orientation so regular pruning of such branches will reduce the likelihood of summer limb drop.
The Link LonkSeptember 10, 2020 at 10:35PM
https://www.ocregister.com/2020/09/10/why-your-flowers-are-dying-and-what-you-can-do-about-it/
Why your flowers are dying and what you can do about it - OCRegister
https://news.google.com/search?q=Flower&hl=en-US&gl=US&ceid=US:en
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