Saturday, December 18, 2010

Not all plants love the rain

Northern California is being pummeled by a series of wet winter storms. The Sierra Nevada is expecting as much as 10 feet—yes, feet!—of snow by Wednesday, and the Sacramento Valley up to 5 inches of rain. 5 inches of rain may not sound all that impressive to some readers, but that’s almost one third of our annual precipitation, which averages between 17 and 18 inches (430-460 mm) a year.

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This is what you see when you stare too closely through a wet window screen.

I had quite a few things I wanted to do this weekend but because of the weather I had to scale down my to-do list. I did take advantage of a break in the weather on Saturday and cleaned up the succulent bed next to our driveway. The cherry plum tree planted between our house and our neighbor’s has been dropping leaves for the past few weeks and this succulent area was covered in a sea of red. With perennials I wouldn’t worry too much about the leaves because they break down relatively quickly and act as insulation against the cold. However, succulents don’t like wet feet, and a thick layer of leaves keeps the soil soggy far longer than it otherwise would. The biggest dangers our succulents face in the winter aren’t prolonged sub-freezing temperatures as much as prolonged periods of wetness.

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Driveway-side succulent bed covered with leaves from our cherry plum tree (Prunus cerasifera 'Krauter Vesuvius')
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Same area after I cleaned out most of the leaves

Using a rake isn’t practical in this area since it would be too easy to damage the plants, so I simply scooped up the leaves with my hands. A thin stick proved useful in cleaning out between agave and aloe leaves. I didn’t try to remove every single leaf—that would have been a Sisyphean undertaking anyway since the cherry plum tree still has some foliage left—but the result is a much nicer-looking bed and hopefully an improved chance of survival for the succulents planted there.

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Agave attenuata x shawii ‘Red Margin’
As I was removing the leaves around the base, I saw a new baby poking its head out of the ground. This is one of my favorite agaves and It’ll be nice to have offsets to share.
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Resin spurge (Euphorbia resinifera) after I cleaned out most of the cherry plum leaves

You can’t really see it in the photos above, but this succulent bed is mounded in the middle, and the most xeric plants are on top of the mound. In addition, we added sharp sand and pea gravel to the soil when we built this bed so drainage is excellent.

However, in spite of these precautions, some succulents will still rot, especially if planted at the base of the mound rather than higher up. This happened to an Aloe brevifolia (common but beautiful) a couple of years ago. I replaced it with Sedum rupestre 'Blue Spruce' (the bluish-green groundcover on the far left in the photo above) because it doesn’t mind the extra moisture.

The most water-adverse succulent I have is an Agave utahensis var. eborispina. Its native habitat are dry, stony outcroppings in the Mojave and Great Basin deserts of Nevada, Arizona and Utah, which get very little rainfall. In contrast to many agaves which don’t mind regular irrigation—some actually thrive on it—this agave is so touchy about water that some collectors grow it in pure pumice instead of soil to ensure perfect drainage. My specimen is still very small. It lives in a 4-inch pot on our front patio and gets watered once a week in the summer, not at all in the winter.

 

Mature Agave utahensis var. eborispina
Photo: http://www.xericgrowers.com

If you have succulents that are particularly prone to rotting during the wet season—like some cacti and aloes—you may need to take extra precautions in the weeks to come, especially if this winter turns out to be much wetter than normal. If they’re relatively small and in pots, the easiest thing would be to move them to an area where they are protected from the rain, like under the eaves of a roof or on a covered porch.

If they’re in the ground, the ideal solution would be to build a tent-like shelter that keeps the area dry. However, I realize that most people won’t go to that length so I’d suggest you simply cover them with a lightweight frost blanket or similar fabric; some water will penetrate but most of it will simply run off. Frost blankets let light and air through and won’t hurt plants even if left in place for longer periods of time.

Clear plastic sheets are OK as well as long as it doesn’t get down to freezing at night; otherwise the plant parts that touch the plastic might get damaged from the transferred cold.

I wouldn’t recommend opaque tarps, such as the ubiquitous blue ones, because they block too much light and hence aren’t suitable for more than a day or two of use. But in a pinch if you have nothing else and a heavy rain is imminent, you can use just about anything that will keep your sensitive succulents dry. Just make sure that whatever cover you use is anchored or weighed down because our winter rainstorms are often accompanied by strong winds.

2 comments:

  1. Winter wetness is a problem here in the Midwest for some plants too, like lavender. Often times if a plant doesn't come back here, winter wet is the reason (as long as it was cold-hardy enough).

    I'm also glad to see that there are some succulents that we both can grow: sedum! I figured that once you could grow the fancy euphorbias, agaves, and cacti you'd shun the lowly sedum. ;-)

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  2. Alan, we have the same problem with lavender. I've lost several over the years. And I can't for the life of my grow ornamental onions (allium). They always rot.

    As for sedum, I love it. There are so many different textures and leaf colors. It truly is one of the most worthwhile genus to grow because it takes whatever you throw at it.

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