We moved to a new house in Castaic twenty-seven years ago.  There is a steep slope in back.  It requires a combination of trees, bushes and ground cover to keep the soil in place. We have sprinklers that cover the entire slope.  The current trees and bushes are doing fine, but we are having trouble finding a ground cover that will tolerate the colder winter temperatures in Castaic.  We currently have red apple (Aptenia cordifolia) ice plant that we have struggled with for the past fifteen years. Every now and then we get frost and temperatures below freezing that kill most of the red apple so it has to be replanted.  We are hoping that you can give us a recommendation for a ground cover that would have the following qualities: 1. Tolerance to cold temperatures 2. Grows quickly; 3. Covers the ground thick enough to choke out weeds.; 4. Holds the soil in place; 5. Won’t have a tendency to grow up into the bushes; 6. Can tolerate light foot traffic once a month for weeding.  We’re not worried about pretty flowers or colors.  We just want it to have most of the qualities mentioned above and items 5 and 6 are the least important.

Rudy and Sandy DePompa

Judging from the photo of your slope, it appears that the upper half is in the sun and the lower half is more in the shade.  Some ground covers, such as red apple, do reasonably well in both exposures.

You might want to consider planting trailing rosemary (Rosmarinus officinalis prostratus) since it can handle both sun and some shade except that you will not be able to walk on it since it gets woody.  Star jasmine (Trachelospermum jasminoides) is also adaptable in terms of light exposure.  However, it too is a woody plant not meant for foot traffic and it will also grow up into other plants unless it is frequently pruned.

An advantage to planting star jasmine, however, is that the very unpredictable and tentacled growth that we often think of as a problem could be useful in covering the ground on your slope, especially if you utilize u-nails to secure the long shoots to the earth.  One issue you haven’t mentioned is the root growth of your mature shrubs and trees and how it will interfere with your ability to make holes for planting.  In such cases, it is sometimes impossible to get any containerized plants into the ground but you have to settle for dirt flats of ground cover where you take pains that each plant, when extracted from the flat, has a small clod of growing media around its roots.  However, if you could manage to insert star jasmine into the ground — and sometimes you can find 4“ or quart size containers where the root ball is not too big — its long shoots could cover a wide area.  A single mature star jasmine, kept at a height of two feet, can grow into a 10 foot evergreen circle of emerald foliage and fragrant flowers.

Another advantage of woody ground covers is that their roots will be deeper and do a better job of controlling erosion than lower growing, but more herbaceous ground cover selections.

Sword fern (Nephrolepis exaltata) is an excellent ground cover for shade and partial sun.  It is one of the few plants recommended for planting under pines since it will accept falling pine needles in between its fronds without complaint.  Sword fern will start looking ratty after a few years but then you cut it back to the ground and it grows right up again thanks to its rhizomes.  The same is true for sweet violet (Viola odorata), another partial sun to partial shade selection that grows from rhizomes but self-sows as well.  Sweet violet does disappear in the heat of summer but pops back up again when temperatures cool.  The only issue with sweet violet is that it’s virtually impossible to find in the nursery trade since it is so easy to grow, some consider it a weed.  Still, you can acquire it from Internet vendors.

You might also consider planting  peppermint (Mentha piperita), spearmint (Mentha spicata), catmint (Nepeta faassenii), and lemon balm (Melissa officinalis), which can all handle some shade and are extremely cold hardy.  They can also absorb occasional foot traffic.

Before embarking on any extensive slope planting project, you might want to experiment with several different ground covers to ascertain which grows best in your particular situation.  All too often, a heavy investment is made in a single plant simply because it appeared on a list of recommended slope selections and its photo was irresistibly seductive.  As someone once said, “you are always a beginner in the garden” and it’s a good idea to exercise caution before making a final determination about what to plant on a huge slope.

As long as we are on the subject of ground cover you can walk on, you really should look at the website of Under a Foot Plant Company.  “Our plants do better when you walk on them” is the company slogan and the website for viewing their plants is stepables.com.  They have actually categorized their ground covers according to their tolerance for being stepped on, whether it’s once a week, once a day, or three times a day.  The video “Sole Mates,” on the bottom right of the website’s home page, is as delightful a garden video as you will ever see.

I was recently in communication with Mike Atkinson, who is long time volunteer for the Southern California Plumeria Society in San Diego and a nationally known plumeria maven as well.  He is also responsible for the www.plumeria.care website.  Atkinson has particular expertise in the area of plumeria pruning and I thought it would be a good idea to have him share his wisdom on this subject.  Plumeria trees, which have the drought tolerance of cacti, are becoming increasingly popular in gardens throughout Southern California.

We are rapidly approaching plumeria pruning season, which extends from March until May.

“Winter is not optimal,” Atkinson writes, “because you can’t root the branches you cut due to dormancy and there’s a chance of moisture getting in to the cut area.”  Pruning from March through May “gives you plenty of time to root the branches you cut off and allows time for new branches to form before the growing season is over.”

I asked what would happen if you just let your plumeria grow and never pruned it.  “An unpruned plumeria just continues to grow,” he answered, “and will eventually be the shape it’s supposed to be. Some plumerias are tall and lanky, some grow more horizontally, some grow down to the ground. Some people like to thin out branches to increase air flow and sun exposure. It can’t hurt, but it’s not necessary, as that doesn’t happen in the wild.”

How careful do you have to be when selecting which branches to prune?  According to Atkinson, “You can shape a plumeria however you want.  Cutting any branch will not harm the plant.”  For example, once a plumeria’s branches were so low that a lawn mower could not cut the grass without bumping into the branches so Atkinson simply removed the lower branches and no harm was done to the tree. “When cutting a branch off the main trunk, there are two options: If you don’t want a branch to grow back, then cut it all way to down to where it connects to the mother plant. If you do want it to branch again, then leave at least a 6-8” stump from the main trunk.”

As for sealing a pruning cut, “I only seal it if I have to make a cut in the off-season,” Atkinson said. “There are many sealers sold for gardening, or just use DAP or Liquid Electrical Tape from the home improvement stores. Also, always cut at an angle to keep water and moisture from settling on mother plant’s cut area. On the branch you just cut off, make a second cut that squares/straightens that angled cut flat, as it will root better that way in the garden.”

Atkinson emphasizes that you should “NEVER use hand pruners, shears, or loppers to cut plumeria branches. Plumerias have a very soft flesh and you can damage it when it’s pinched by these cutting tools. And don’t use a saw with large, wide teeth. A hand saw with a very thin saw-toothed blade like a hacksaw is perfect.”

Tip of the Week:  Atkinson urges us to “Please never throw away cut plumeria branches. Share some aloha by giving them to others. Let neighbors, friends, and family know you have them. Or just set them out by the curb. The plumeria societies in San Diego and Anaheim offer free pruning services in exchange for donating most of the cuttings to them. Contact them through their websites at socalplumeriasociety.com and southcoastplumeriasociety.com.”