Bahia- soil amendments, clay tolerant succulents?

12 years ago

Bahia, I am curious what particular ammendments you use to improve drainage for succulents here in the Bay Area with heavy clay soils.

I am in El Sobrante with a flat lot.

Also what are some of the most clay tolerant varieties, I read somewhere you said Aloe Thraskii was particularly tolerant of our wet winters... what are some others?

Thanks, and anyone else feel free to chime in!

Featured Answer

bahia

12 years ago

Aloe thraskii might be a bit too cold sensitive for El Sobrante, as parts of your town get significantly colder than Berkeley/Oakland, and this species isn't amongst the most freeze tolerant of the tree aloes; better to stick with Aloe marlothii or A. ferox or A. arborescens.

In general, it is always better to mound the soil if you have this option to give better drainage with heavy clay soils on a flat lot. Just creating mounds that are 12 to 18 inches above the flat parts is often all that is required to improve your drainage. There are lots of succulents that will tolerate straight clay soils if they slope to drain, but adding and mixing in at least 2 to 6 inches of soil amendments won't hurt, and American Soil Products multi-purpose or general landscape mixes work well. If you have your heart set on species that are more demanding, then add some perlite and pumice to the mix at individual planting holes, and make sure more sensitive plants are planted higher up on mounds rather than in low points. Full sun during winter and good air exposure also help to make plants more tolerant of winter wet and clay soils.

In general, succulents that come from winter rainfall habitats will be more broadly tolerant of poor soil conditions, and your best clues will be observing which succulents do well in your neighborhood.

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Comments (8)

calistoga_al ca 15 usda 9
12 years ago
Other than addressing a drainage problem, I can not tolerate gardening on a flat lot. I am willing to pay the cost of a few yards of top soil to get away from that flat boring surface in which all the plants have the same emphasis. An undulating garden is so much more fun. Al
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jenn
12 years ago
I'm glad you asked this question, Elvie.

A question about the mounds: how do you keep the mounded soil from sliding downward? I'm assuming the mounds are wide enough with the plant in the center which is supported by the soil on the outside, and some of the outer soil will be lost as it slides down the pile.
Dick_Sonia
12 years ago
I have quite a few raised beds/mounds. Jenn is absolutely correct. Gravity, rain, wind and soil organisms are Nature's graders. Keeping mounds topped up is a continual chore. Rain will constantly erode your nice sloped sides and pretty soon you have exposed root crowns. Building soil is a chore anyway, so I keep at it. Eventually you'll get enough mass in the center that it will form a plateau and be somewhat less maintenance. As the slope of the perimeter around the sides of the mound gets lower and lower, erosion finally slows.

Some kind of containment works best. This can be either formal or informal. I've used sawed-off lengths of 4-5" branches pounded into the ground at varying lengths (time-consuming, but looks okay), stones and bricks. You can also just build a low framework of scrap wood as a stop-gap measure while succulents with a spreading habit planted around the perimeter get established (the wood will eventually just rot away). Plant roots work wonders for holding soil. Remember that the mounds don't need to be that tall. If you use scree beds instead of clay mounds they can be shorter still.
jenn
12 years ago
dick_sonia: Thank you for the explanation; I've been wondering about this for a long time!
elvie z9CA
Original Author
12 years ago
Thanks for your feedback Bahia and everyone.
bahia
12 years ago
Mounds don't erode or slough off if you give them sufficient room. 5:1 slopes,( one foot of rise in five feet of run) is plenty stable, and even more so if heavily planted and also mulched. We don't get intense and/or prolonged rains to create problems with gentle slopes. Most people seem to think a "mound" is more like a hump, and don't make them wide and gradual enough. The photo I am linking to here has mounds up to 18 inches above the sidewalk in the foreground, and is almost entirely planted with succulents and then mulched. There has been no erosion at all, after 3 years upon initial planting.

Here is a link that might be useful: Mounds with succulents
hoovb zone 9 sunset 23
12 years ago
An undulating garden is so much more fun. Al

Amen. I was uneasy when we moved to a hillside home, but now I'm happy with all the slopes. They make every plant visible.