Planting on a Bank & Best Substitutes for Lawns
Question from Howard:
We are a Homeowners association with a steep bank, 45 degrees or steeper, three blocks long and about 30 feet high. What drought tolerant plant(s) would you recommend? Also, what ground cover, if any, would you recommend to replace grass areas?
Answer from Pat:
Before I can answer your question, I need to know where you live. Plants are adapted to certain regions and not to others. I cannot give you any suggestions for what to plant without knowing where you live. For example, what if you live in the Middle West, or Arizona, or New England? Your question gives me no clue. My recommendations for planting a bank in each of these regions would be totally different. Also, if you live in Southern California, or anywhere in the west, please tell me what Sunset Climate Zone you live in. (Please do not give me the USDA Climate Zone since they are not specific enough.) If you give me your Sunset Climate Zone, I will know what plants to recommend. Also, please refer to my suggestions to other readers who have written with questions about planting a bank. Perhaps I have already described a bank planting that will perfectly fill your needs. You will find many suggestions included in the answers given on the following link: Plant to Prevent Erosion on a Steep Hillside.
Hi Pat,
I live in La Jolla, CA, near the coast on Mount Soledad. My lot has a very step slope, which appears to have been stable for the 30 years since the house was built there. The slope has an L shape facing east and south. There currently are 2 large Brazilian pepper trees, a California pepper tree, and a couple of oleander bushes. The soil is clay.
Any suggestions for ground cover, which would help hold the hill and provide color through the year, would be appreciated.
Also, we would also like ideas for replacing grass on level surfaces around the house.
Thanks,
Greg
As far as I am aware, slippage on Mount Soledad in the past has resulted from geological and human factors, such as sloping substrates of rock that shed water. When the clay layer above gets soaking wet due to heavy rains combined with bad drainage or from broken and leaking pipes, the upper strata of clay-based top soil can slip downhill over the lower rock layer. When the “toe” of the top strata at the bottom of the slope has been cut through, this action can also de-stabilize a slope since cutting through what might be an ancient landslide leaves the upper portion of the slope with nothing to lean on down below. Such events are tragic and could largely be prevented. No tree or ground cover is capable of holding a top layer of soil in place under these circumstances. I would hope the south-eastern slope of Mt. Soledad where you live will never suffer this problem. It’s always good to be vigilant, keeping an eye out for any visible problems and making sure these get promptly fixed if not by the city, then by the community.
Brazilian pepper (Schinus terribinthefolius) and California pepper tree (Schinus molle)—the latter is actually native to air-drained slopes of the Andes Mountains in Peru—, are both drought-resistant trees once established, though California pepper needs less water than Brazilian pepper. Both have invasive roots that make it difficult or sometimes impossible to grow anything under their shade canopies. Their roots do not go deeply into the ground but inhabit the top layer. Brazilian pepper puts up many annoying suckers from its roots but each of these trees can become extremely picturesque in age. You also have oleander, which suffers from glassy winged sharpshooter which for several years has been inoculating oleander with a dread bacterial disease, Oleander Leaf Scorch (Xylella fastidiosa), that is currently killing many oleanders throughout Southern California and Texas. Some day you may need to replace these with some other shrub.
Given the characteristics of your pepper trees, the best option for your bank would be to choose a variety of tough shrubs to grow there as well as some lower ground covers. I have already made a few suggestions to other people who have written me with similar questions. Read those answers and take those ideas into consideration along with what I am going to suggest to you.
For a colorful ground-cover on your hillside, one option would be for you to spring for a more expensive and designer look that is very trendy today, which would require amending the soil to make it drain better, then nestling a few large boulders into the ground, adding a dry stream bed and planting a wide range of aloes, agave’s, ice-plants, and succulents. I have covered a large bank in this way and it is a popular and enjoyable way to deal with slopes. Though clay soil may not be the ideal soil for succulents, these plants can adapt to clay especially if it is well-amended and on a bank there is the benefit that any excess water will drain off. On page 22 of her popular and extremely well-illustrated book, “Designing with Succulents”, Debra Lee Baldwin says, “At the Santa Barbara Botanic Garden heavy clay soil is amended with compost, gravel, sharp sand…and wood chips.” (Sharp sand means very gritty stuff like coarse decomposed granite.) I would also add gypsum. (As a general rule I do not believe in adding sand to clay so I would also leave out the sand.) If you’re interested in this approach study the photos in Debra’s book. Any of these schemes can be more or less copied.
If you’re not in the mood for the work and expense involved in the above idea, how about covering your entire bank with ground-cover types of bougainvillea, blue plumbago ‘Royal Cape’ or ‘Imperial Blue’, and lantana ‘Radiation’? This mix will give you gang-buster color year-round and can take any soil. Cover any bare bits of ground with yellow trailing gazanias until the larger plants take over.
Here is a third idea: For the easiest care of anything, cover the entire bank with a variety of trailing lantanas, especially Lantana montevidensis which is a lovely lavender color. Lantana will cover the bank quicker than bougainvillea and plumbago will. Trailing lavender-colored lantana (L. montevidensis) also mixes well on a bank with white, yellow and orange low-level, ground-cover-type lantanas. (Read about the varieties and their various characteristics in Sunset Western Garden Book.) You will have a lot of color most of the year and it’s really the easiest way to go. There is also the newer hybrid ‘Patriot Series’ of lantana, which is more compact than old types and thus it makes a good lower ground-cover but may be more expensive than older varieties. ‘Patriot’ lantana comes in combinations of yellow, pink, purple, orange and red.
For a drought-resistant lawn substitute on flat areas near the house, how about planting lippia (Phylla nodiflora)? Lippia (or Phylla as it is now called), is drought-resistant, grows exceptionally well near the coast, stays green year-round, and is covered with pretty, little pink flowers in June. It is reputed to look less good in winter, but along the coast this doesn’t seem to be true. I think it is the most under-rated plant there is. No one seems to know that it makes a fine lawn substitute. It takes quite a bit of foot traffic without any perceivable problem and you only need to mow it once or twice a year if that. If you have dogs mow off the flowers in summer, since they bring bees and your dogs may step on them and get stung. However the bees won’t bother people wearing shoes. I have often walked on it with no problem. Bees seem to get out of the way and anyway they have no desire to bite us.
Alternatively, you might like a lawn of common yarrow (Achillea millefolium) mixed with wildflowers. Plant both the yarrow and the wildflowers from seeds this fall. Pull out the wildflowers after they fade. Mow off the yarrow flowers with a weed wacker once a year after flowers fade and rake up the remains. Water once in a while when rains aren’t adequate. This makes a very fun lawn substitute and you will have lovely flowers for the house. For variety, plant other types of yarrow in with the A. millefolium if you wish. Yarrow will spread quicker if you feed it to speed it up a bit. Once it covers the ground, stop feeding it or it will become invasive. Also plant some South African bulbs in there this fall. It’s fun trying out different things and seeing what will grow. Since you have clay soil, prior to planting wildflowers, I would amend the soil well with organic soil amendments and soluble gypsum. Wildflowers prefer well-drained sandy soil, but Achillea is less fussy and Lippia is even less bothered and often thrives in clay since clay soil seldom has nematodes. Nematodes are a genuine problem for Lippia in the desert where it’s most often grown.