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  • Writer's pictureDebbie Gliksman

Loving our Plants to Death

Plants need water to thrive so if you want them to grow extra well you should give them

extra water - right? Wrong. As it turns out, giving plants too much water is just as likely

to kill them as not watering at all. This is especially true when it comes to using

California native plants or California climate-appropriate plants. Why? Because they

were simply not meant to have a lot of summer water. After all, the hallmark of the

Mediterranean climate zone is wet winters and dry summers.

Your plants will seemingly look healthy one day and the next day the leaves will start to

droop. Time for more water? Not necessarily. If they are suffering from Phytophthora, a

soil-borne pathogen that infects trees, woody plants, and even vegetables, more water is

the last thing that they need. Because water, especially in the warm days of summer

when the pathogen can spread easily, is what’s causing them to die.

The name Phytophthora comes from Greek - φυτόν (phytón), "plant" and φθορά

(phthorá), “destruction”; and means "the plant-destroyer". It’s a genus of plant-damaging

oomycetes (water molds), and it’s a gardener’s worst nightmare. (One strain of

Phytophthora, known as Phytophthora Infestans, was the fungal agent responsible for

the Great Irish Potato Famine.)

Phytophthora attacks the roots of a plant or tree, making them unable to absorb

nutrients or water because of the dead root tissue. Preventing the spread of

Phytophthora is difficult, but possible. Since the mold thrives in water, the most

important aspect of prevent is correct water management. Water should be uniformly

distributed to each plant, without causing the plant to stay wet for unnecessary amounts

of time and your irrigation system should be moving the water away from roots.

Sometimes the results can happen almost overnight; sometimes it takes a while,

causing weakness and a slow collapse in the affected plants over a course of months or


Poorly draining soil can exacerbate the problem because phytophthora only needs four

hours of standing water to germinate. In clay or compacted soils, it helps to plant on

mounds 8 – 10 inches tall. But phytophthora occurs in all types of soils. In fact, I

encountered it in a garden with very sandy soil.

Although there is no cure for Phytophthora, there is a way to prevent and treat it. I spoke

to Jerry Turney, Los Angeles County Plant Pathologist to learn more about it.

Unfortunately, plants that are already stricken need to be removed quickly and disposed

of carefully so that you don’t spread the pathogen. But what about the plants that are

left that are showing signs of failing?


Jerry’s advice was to apply a solution called Phosgard. It is available from Leaf Tech 1-

800-350-5323. Here’s how to apply it:

1. Move your mulch away from the base of the tree or plant when applying so that

the solution will go straight into the soil around the plant. (Replace when

afterward but remember, as always, to keep your mulch layer away from the

base of your plants and trees.)

2. Dilute the Phosgard solution at a rate of 1 tbsp. per gallon (1/2 oz) and soak the

soil around the affected plants weekly during summer and monthly through the

winter. If there is a lot of precipitation, reduce the frequency because you don’t

want your soil too saturated - wet soils encourage phytophthora root rot.

3. Once the plants show some good growth you can reduce the frequency to every

three months. Watering can be reduced to once a month in spring and every two

weeks (if necessary) in summer.

4. You can also spray the plant foliage with the diluted Phosgard solution.

5. Mulch twice a year and add gypsum to the soil (gypsum should go underneath

the mulch).

6. He also suggests using mycorrhizae on the root ball of when planting.

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