“For years ivy has flourished on our hillsides. This year, most of the ivy on the hillsides has died or withered and weeds have overtaking the ivy. The ivy is about 50 years old and receives full sun and no water in the summer. However, this has never happened before and it is happening to everyone’s ivy. There is always a time in the summer when the leaves burn and are brown for a period of time but, prior to this year, the ivy has always recovered.Have you any idea what has caused this problem? Do you think the rain will revive the ivy? What is a good plant for steep hillsides if we need to replant?”
Nancy Petersen, Rancho Palos Verdes
I would definitely give it a chance to rejuvenate a little while longer, considering all the rain that has blissfully come down this winter. If it doesn’t rejuvenate on its own, you could cut it back to ground level. After such a radical pruning, I do believe it would eventually cover the slope again, although this could take some time.
Both English ivy (Hedera helix) and Algerian ivy (Hedera canariensis) are native to Europe and the Mediterranean. English ivy arrived in America in the 1700’s as an ornamental addition to colonial gardens. Algerian ivy has a floppier leaf and is more tropical, yet more drought tolerant than English ivy. Although it is still available in nurseries, ivy has become an invasive pestilence in the United States in the Northeast and in the Pacific Northwest as well. While ivy is considered invasive in Los Angeles County, our long and dry summer keeps it from gaining a foothold in what remains of our local wilderness. Yet ivy has its advocates, too. Thanks to the American Ivy Society, you can examine and procure 75 different ivy cultivars, many of them with tiny leaves and interesting variegations, at www.ivy.org. Although it was once considered to be a plant that prevented soil erosion on slopes, this has not proven to be true.
After many years of growth, ivy — in the manner of Bermuda and other tropical grasses and many ground covers, too — builds thatch (a layer of obsolete or senescent stems) which prevents penetration of water into the soil and down to the roots. If all the ivy in your neighborhood is showing similar signs of stress, it could be that all the ivy is as old as yours and therefore would be susceptible to the same thatch build up. It is a lot of work cutting ivy to ground level but it’s the only way to resuscitate it after growing in a particular spot for a long time.
If you want to replace it, you will need to plow up your slope in a serious way — through hand pulling, roto-tilling or a combination of both — in order to remove as much of the roots as possible. Even then, you will need to patrol the area on a regular basis to pull out any ivy that grows back up. Some gardeners have taken a blow torch to their ivy with satisfactory, if not quite permanent, results. If, over a period of months, you blow torch each time new growth appears, your chances of eradication.increase. Solarization, most effective in hot weather, is another option. After removing ivy to ground level, soak the area and then cover and seal it with transparent plastic. The steam heat trapped under the plastic kills anything that grows there.
Chemical solutions are available but, especially if we are talking about a large expanse, you might want to hire a professional landscape company or arborist that sprays for horticultural issues. Since ivy has a waxy leaf, even broad spectrum herbicides such as Roundup will not kill it. Research has also shown that where replacement of ivy with native plants, whether from seed or containerized specimens, is desired, preliminary hand-pulling of ivy as opposed to chemical spraying, is most effective as a preliminary measure to establishing the natives.
The good news is that, where ivy once grew, the soil is soft and easily planted due to aeration and oxygenation provided by ivy roots. Your Rancho Palos Verdes neighborhood also has a favorable ocean moderated climate so that almost anything will grow there. The fact that ivy, which is typically planted in the shade in hot interior climates, has long prospered in full sun in your area is evidence of a benign microclimate that will support the full pallette of arid zone and sub-tropical plant species.
You could replace your ivy with a low growing California native ceanothus such as ‘Yankee Point’ or ‘Carmel Creeper.’ Other native possibilities include California fuchsia (Zaushneria california), lemonade berry (Rhus integrifolia), sugar bush (Rhus ovata), brittle bush (Encelia farinosa), and toyon (Heteromeles arbuitfolia).
You might consider a low growing bougainvillea such as ‘Raspberry Ice’ or encourage a typical large vining type to grow as a ground cover by holding down its long shoots initially with u-nails plunged in the soil and then pruning it every now and then to discourage vertical growth. Other options would include lantana, Myoporum parvifolium, trailing rosemary, ornamental grasses, and Acacia redolens ‘Low Boy.’
Silverberry (Elaeagnus pungens) is a shrub that is a personal favorite of mine. It can grow up to fifteen feet tall and wide but is drought tolerant, fast growing, and seemingly immune to all pests and diseases. I recommend it for slopes since it’s a plant that you never need to worry about once it’s in the ground. It just grows. There are variegated types with green and silver or green and gold foliage. Silverberry also has fragrant, if non-descript, flowers that bloom in the fall. Fruit is edible and seeds, once their fibrous covers are removed, may also be eaten. Silverberry does not need to be fed since, in the manner of legumes, it provides its own nitrate fertilizer with the assistance of symbiotic bacteria that dwell in its roots.
“We have very mature redwoods and suddenly one of them with a double trunk appears to be dying. This has happened literally within the last two weeks. It is just so odd since we gave all the redwoods extra water over the past summer, and then about 2-3 months ago, we cleared all the ivy that was growing beneath them. However, in clearing the ivy, we also removed the redwood detritus that had collected between the ivy. The trees are about 30-40 years old. Still, the other redwoods, which are nearby, look healthy.”
Joyce Nussbaum, Hidden Hills
When one tree suddenly weakens and other nearby trees of the same species are fine, you naturally suspect some sort of root borne fungus and are concerned that the fungus might spread. Redwoods in our area, however, are not known for suddenly dying from a fungus disease. However, redwoods can suddenly turn brown when water deprived. Redwoods are known for their shallow but dense root systems and so removing their ivy detritus or protective layer of mulch could have contributed to their current stress. After the recent heavy rains, they should show some signs of revival if they are still viable trees. Make sure to keep a four inch layer of mulch on the ground around your trees at all times.
Tip of the Week: If you suspect any tree or shrub is suffering from drought stress, and its roots are dense or the surrounding soil is compacted, consider watering with a deep root irrigation device. A deep root irrigator is simply a pipe that comes to a sharp point. You insert the irrigator into the root zone of your tree or shrub after attaching a hose to it. After allowing the water seep into one area of the root zone, move it to another area and then another until the entire root system has gotten a good drink. Repeat this procedure every few days until, hopefully, the plant begins to sprout fresh green shoots again.