Hillsides in Pasadena can be gorgeous, but they also move. Winter storms pour out of the San Gabriels, carving rills into bare soil. Long, dry summers shrink fine clays to dust. If a slope is poorly rooted, one afternoon squall can loosen a surprising amount of earth. The goal is not to fight the hill, it is to help the hill hold itself together. Plants do that work better than anything else, when you match the palette to the site and install it with care.
I have planted and maintained slopes from Linda Vista to Hastings Ranch, and the same truths show up again and again. Deep, fibrous roots beat shallow roots on loose decomposed granite. Plants that knit laterally stop rills before they start. Rainwater needs a place to soak and spread out, not shoot straight downhill. And a hillside planting only pays off if it is maintainable, drought resilient, and wildfire smart. The palettes below come from that lived experience, tuned to Pasadena’s Mediterranean climate and the mix of chaparral and urban conditions that define our hills.
Why plants are the first and best erosion control
Gravity never gets tired. You slow it with friction, texture, and roots. Mulch and jute help in the first storm cycle, but roots do the real work by:
- Binding particles at multiple depths. Grasses and sedges weave the top 6 to 12 inches. Shrub roots reach 2 to 6 feet, anchoring the matrix. Softening rainfall impact. Foliage turns hammering drops into dripping beads, so soil does not crust and shed water. Slowing overland flow. Stems and leaves roughen the surface, which drops velocity, which drops the water’s ability to carry soil. Increasing infiltration. Organic matter and root channels invite water down instead of out.
Hardscape features have their place. A well engineered retaining wall, steps, or a stone check terrace can break up long runs and protect structures. But even the best wall benefits from planting above and below, because roots stabilize the zones that engineering cannot reach and keep stormwater from digging behind or beside the structure.
Know your slope before you choose a palette
Every hillside has microclimates. Pasadena has north slopes that stay cool and mossy after a wet year, and west slopes where chaparral bakes in August. What matters most when you pick plants are four interlocking conditions.
Sun and heat. A west or south facing exposure gets punishing afternoon sun and radiant heat off walls and paving. That spot fits tough coastal sage scrub plants like California buckwheat and black sage. A north or east aspect suits manzanita and some ceanothus better.
Soils. Much of our foothill soil trends to decomposed granite with outdoor lighting pasadena fast drainage. In older neighborhoods, you also find imported topsoil over clay, or fill soil over compacted subgrade. Dig a few test holes. If water still sits after 12 to 18 hours, you have drainage issues and need species that tolerate heavier soils, or you need to amend strategically and add perched swales to slow and infiltrate.
Slope angle and length. A 2 to 1 slope, about a 50 percent grade, demands tighter spacing, denser groundcovers, and temporary netting. Long uninterrupted runs over 20 to 30 feet amplify speed and erosion, so break them up with terraces, boulder bands, or planted berms.
Irrigation access. Permanent overhead sprinklers on slopes waste water and cause runoff. The most reliable system is drip with pressure compensation, staked closely to emitters so the lines do not creep downhill. If you cannot run new drip, plan a deep hand watering regimen for the first two summers, then taper off.
The traits that stabilize a Pasadena hillside
I look for five plant behaviors when building an erosion control mix for our area.
- Root architecture that holds both surface and subsoil. A blend of clumping grasses, running grasses or sedges, and shrubs gives redundancy. Deergrass, purple three awn, and coyote brush cover different depths and textures. Canopy that drapes and grips. Plants like California buckwheat and trailing rosemary grab the ground and knit neighboring plants, so you do not see bare arcs between root balls. Drought survival with honest establishment needs. Most California natives need regular water the first one to two summers to set roots. After that, they cruise on seasonal rain with minimal supplemental irrigation. If a species needs weekly water forever, it is a liability on a slope. Fire wise growth habits near structures. Within the first 5 to 30 feet of a building, choose plants that keep low, retain moisture, and do not shed fluffy, resinous litter. You can still go native, just manage spacing and seasonal cleanup. Wildlife compatibility. Pollinators and birds are not a bonus, they are part of the system. Plants that feed them also tend to be the tough, regionally adapted species that hold soil best.
Smart installation on slopes, step by step
Here is the sequence we follow on most Pasadena hillside installs, sized for a typical 800 to 2,000 square foot slope. Adjust to your site and access.
Shape water first. Cut shallow swales on contour, about 4 to 8 inches deep and 18 to 24 inches wide. On long runs, add rock or log check dams every 10 to 20 feet to slow flow. Avoid steep notches that concentrate runoff. Set erosion controls. Stake jute netting top to bottom so rows overlap by 6 to 8 inches, or use biodegradable coir blankets on very steep sections. Lay fiber wattles along the contour above paths, drain outlets, and at the top of the slope to intercept sheet flow. Plant through the fabric. Cut an X just big enough for the root ball. Set plants high rather than deep so crowns do not rot. Backfill firmly to remove voids, then tuck fabric back around the stem. Install drip and mulch. Run 1 2 inch header lines laterally, 0.6 gph pressure compensating emitters at 12 to 18 inches from stems for shrubs, 6 to 8 inches for grasses and groundcovers. Cover exposed soil with 2 to 3 inches of shredded mulch, not on top of the crown. Water to settle, then monitor. Give each plant a slow soak to saturate a 12 to 18 inch depth. For the first season, deep water 1 to 2 times monthly in cool months without rain, 2 to 4 times monthly in hot months, adjusting to real weather.Seasonal timing that works here
Fall is the best time to install erosion control plantings in Southern California. Aim for late October through December, near the first soaking rain. Cool weather and periodic storms nudge roots deeper without heat stress. If winter runs dry, water deeply once a month so roots keep exploring. Spring installs can work when you have drip ready to go on day one, but expect more visits through the first summer. Avoid peak heat starts if you can. A March to April install can succeed, a June start requires more labor and water to get the same results.
Pasadena friendly plant palettes for real slopes
The mixes below lean heavily on California natives, with a few well behaved Mediterranean accents that play nicely in our climate. Spacing is not a fixed rule, it is a starting point. On steeper ground, go tighter. Around walks and patios, give more room.
| Palette | Where it fits | Core species | Spacing guidance | | --- | --- | --- | --- | | Full sun chaparral binder | Open, south or west facing slopes with fast drainage | California buckwheat (Eriogonum fasciculatum), black sage (Salvia mellifera), coyote brush dwarf forms (Baccharis pilularis ‘Pigeon Point’), deergrass (Muhlenbergia rigens), purple three awn (Aristida purpurea) | Shrubs 4 to 6 feet on center, grasses 24 to 36 inches, groundcovers 24 to 30 inches | | Hot wall or driveway edge | Radiant heat zones beside stucco, masonry, or paving | California lilac compact forms (Ceanothus ‘Yankee Point’ on roomier slopes), Cleveland sage (Salvia clevelandii), trailing rosemary ‘Irene’ or ‘Huntington Carpet’ as an accent, verbena ‘De La Mina’, Catalina fuchsia (Zauschneria/Epilobium canum) | Shrubs 5 to 7 feet, groundcovers 24 to 30 inches, accents 24 inches | | Morning shade, afternoon sun | East aspects, light reflected heat | Toyon juvenile hedge (Heteromeles arbutifolia, pruned to multi trunk), island alumroot clumps (Heuchera maxima) in pockets, globe mallow (Sphaeralcea ambigua), California fescue (Festuca californica) | Large shrubs 6 to 8 feet, perennials 18 to 24 inches, fescue clumps 18 inches | | Under coast live oak canopy | Dappled light, dry summer shade, no summer overhead water near trunk | Fescue mix (Festuca idahoensis ‘Siskiyou Blue’ and Festuca californica), chaparral pea (Pickeringia montana, limited use), coffeeberry dwarf forms (Frangula californica ‘Eve Case’ or ‘Leatherleaf’ forms away from trunk), evergreen currant (Ribes viburnifolium) | Groundcovers 18 to 24 inches, shrubs 5 to 7 feet, keep drip lines outside oak’s critical root zone irrigation in summer | | Shady north slope | Cooler, slower draining sites | Manzanita groundcover forms (Arctostaphylos ‘Emerald Carpet’, ‘Pacific Mist’), snowberry (Symphoricarpos mollis) in moister pockets, seaside daisy (Erigeron karvinskianus) as an accent, Douglas iris (Iris douglasiana) | Manzanita 4 to 6 feet, shrubs 4 to 5 feet, perennials 18 inches | | Seasonal swale and toe of slope | Intermittent wet areas, where water slows and sinks | Juncus patens, California gray rush; deergrass; creeping wildrye (Elymus triticoides); California goldenrod (Solidago velutina ssp. Californica) for pollinators; redtwig dogwood only in the wettest pockets near runoff outfalls | Grasses 18 to 24 inches, larger rush clumps 24 to 30 inches, shrubs 6 to 8 feet | | Rocky decomposed granite bank | Rubbley, fast draining slopes | White sage (Salvia apiana) used sparingly, low profile buckwheat varieties (E. Fasciculatum ‘Dana Point’, ‘Saffron’), desert mallow, Dudleya species tucked into rock faces, California sunflower (Encelia californica) | Shrubs 4 to 6 feet, perennials 18 to 24 inches, Dudleya 12 inches | | Fire wise near structures | First 5 to 30 feet from buildings, with regular maintenance | Low growing buckwheat, Cleveland sage kept open and limbed up, yarrow (Achillea millefolium) as a green carpet in irrigated pockets, cistus hybrids as non native fillers where appropriate, manzanita groundcovers | drought tolerant landscaping Keep mature heights under 3 feet near the first 5 feet, spacing to maintain 2 to 3 feet between mature canopies |
A note on ceanothus and manzanita in the basin. Many forms are happiest when planted in fall into quick draining soils and watered sparingly after the first summer. Heavy summer water or compacted clay around their crowns can shorten their lifespan. If you have a flatter bench with clay fill, consider coffeeberry or toyon over a large manzanita, and choose the spreading manzanita forms only where drainage is strong.
How a mixed palette stops rills and slides
Monocultures fail on slopes. A full carpet of trailing rosemary looks good for two or three years and then opens up with age, inviting erosion right when you expect stability. A better hillside usually blends three roles.
Binders at the surface. Festuca, Elymus, and Juncus add a felt of roots that resists the first push of sheet flow.
Knitting shrubs. Buckwheat, coyote brush dwarfs, and ceanothus spread and overlap canopies, creating shade that slows weed germination and keeps soil softer and more absorbent.
Anchor points. Deergrass and toyon, placed like pins across the slope, reach down into the subsoil. When we get an atmospheric river and see rivulets cut for a day, the big roots keep the hillside from migrating.
This mix also builds seasonal interest without fuss. Pasadena gardens deserve color that matches our architecture. Buckwheat’s pink to rust umbels, Cleveland sage’s perfume, and Epilobium’s late summer firework blooms read beautifully against Craftsman shingles and Spanish Colonial stucco. That is not decoration. It is a signal that your erosion control is alive, diverse, and working.
Irrigation that protects slopes, not undermines them
Drip is your friend on a hill. It targets water to each root ball, reduces runoff, and qualifies for many water efficiency rebates. The SoCalWaterSmart program has, in recent years, offered incentives for smart irrigation controllers and rotating nozzles. Check current offerings before you upgrade, especially if you plan to replace a lawn with drought tolerant planting on an adjacent flat area.
Set expectations early. Even drought tolerant natives need consistent moisture for the first dry season or two. After establishment, many Pasadena slopes get through summer on monthly deep waterings or less, especially on north aspects. A few rules of thumb that have held up in the field:
- Water deeply, not often. Encourage roots to chase moisture downward. Short, frequent waterings keep roots near the surface where soil is weakest. Adjust by aspect and species. A west slope with sages and buckwheat needs more summer water than a north slope of manzanita, assuming similar soil. Watch the plants, not the calendar. Wilting at midday is not a crisis if leaves rebound by evening. Persistent morning wilt means you have waited too long. Avoid overspray and runoff. Overspray on slopes is a double loss. It wastes water and erodes the very soil you are trying to protect. If you still have old pop ups on a hillside, convert them.
If you install a smart controller, set custom schedules for slope zones. Many controllers have a slope setting that lengthens soak times and inserts pauses so water can infiltrate between cycles, a big help on the coarser, granitic soils found above the Arroyo.
Avoiding the irrigation mistakes that undo good planting
I have seen more hillside failures from water than from plant choice. Three consistent troublemakers:
Watering too soon after heavy rain. Saturated slopes need time to drain. Adding irrigation before the soil has firmed up can trigger surface slumps and suffocation of new roots. Give it a few dry days, then deep water sparingly if the root zone dries.
Burying crowns under mulch and wetting them daily. A 2 to 3 inch mulch layer is helpful, but not on top of stems. Keep a palm sized ring clear around each plant. Daily wet crowns encourage rot, especially on ceanothus and manzanita.
One zone for sun and shade. Mixed exposures on a single valve guarantee that something will suffer. Separate a hot upper west face from a cooler lower north pocket, even if it means one extra valve. You will save water and replant costs the first summer.
Soil preparation without overdoing it
A hillside does not need rich fluffy soil. In fact, too much amendment can create a sponge on top of a pan, which turns into a slip plane during storms. On most Pasadena slopes, the best prep is modest.
Open the planting holes wider than the pot and only as deep as the root ball. Rough the sides so roots can explore. Blend in a small amount of compost with the backfill, maybe 10 to 20 percent by volume, especially if you are planting perennials. In very coarse decomposed granite, a shovel or two of loam in the hole can reduce initial leaching and help the first roots find purchase. Skip fertilizers at install. A light top dressing of compost under mulch in the second spring usually does more good.
Where the slope has compacted fill, rip shallow grooves on contour with a mattock to break tension and give water purchase. If you can insert a spade fully with moderate effort, you have enough tilth to plant most natives successfully.
Integrating hardscape the smart way
Not every slope can be stabilized with plants alone. On older Pasadena properties, downslope fences and patios sometimes trap runoff and force water into a narrow band. If you see concentrated flows, address those with grading and hardscape before you plant.
Terraces and steps. A series of low, 12 to 18 inch terraces can turn a treacherous 2 to 1 face into comfortable benches where plants establish easily. In the San Gabriel Valley, I prefer dry stacked stone or concrete block with proper drainage to solid mortared walls on small residential slopes. They flex a bit and relieve pressure during big storms.
Retaining walls where required. For taller drops near property lines or structures, consult an engineer. The best retaining wall materials for Pasadena hillside homes tend to be concrete masonry units with geogrid reinforcement, or engineered block systems that are rated for your slope conditions. Natural boulder walls fit the Craftsman and Spanish Colonial vocabulary nicely and perform well when properly keyed in.
Paths and landings. Safe access simplifies maintenance. On steep slopes, decomposed granite with a stabilizer, set into gentle cross slopes and edged with stone, gives workers and homeowners a way to weed, prune, and adjust drip without sliding. If you are debating paver patio vs concrete patio for an adjacent flat zone at the slope base, know that permeable pavers with an open graded base will move less water across the surface and into your planted toe.
Fire wise spacing without sacrificing beauty
Erosion control and wildfire resilience work together. Keep the first 5 feet from structures lean and green, with low, well hydrated plants and non combustible mulch like gravel or stone bands. From 5 to 30 feet, group plants in distinct clumps separated by open space or low groundcovers. Limb up shrubs like Cleveland sage to show clean trunks and reduce ladder fuels. Remove dead flower heads on buckwheat once they have fed the birds, or leave a portion for seed and prune the rest. A seasonal cleanup in late summer when the dry heat arrives pays dividends in both fire safety and plant vigor.
Real results, not just plant lists
A client above Arroyo Boulevard had a 40 foot long, 20 foot high west facing slope that lost soil onto a driveway every January. The soil was coarse DG with a thin skin of imported topsoil on top. We shaped two shallow swales, set wattles at the top, and netted the face. The palette was simple: deergrass on a 4 foot grid, low California buckwheat in the mid zone, and coyote brush ‘Pigeon Point’ near the toe where the driveway reflected heat. We tucked Aristida purpurea into the gaps and planted Epilobium along the top swale. Drip ran along each contour, with 0.6 gph emitters near crowns and one extra emitter upslope of each shrub on the steepest section.
The first winter, heavy rain cut two small rills that ended at our check dams. We patched the rills with leftover mulch, bumped the emitter runtime by 10 minutes for the following cycle, and saw no new movement. By the next fall, the plants had woven a mat. Two years in, irrigation ran every 14 to 21 days in July and August, then off from late October to April. The driveway stayed clean through storms that flooded lower parts of town. That is not magic, just a good match of plant behavior and water management to a specific Pasadena hillside.
Maintenance that keeps the hill stable
An erosion control hillside is not set and forget. It is low maintenance, not no maintenance. The most effective routines are simple and seasonal.
Weed early, especially in year one and two. Annual grasses and mustards are opportunists that find the smallest gap. A 15 minute walk after the first rain, pulling seedlings, is worth hours later.
Mulch refreshers in spring. Top up to 2 inches where wind and gravity have thinned it. Avoid burying crowns. In swales, keep mulch thin or switch to rounded gravel to prevent float and clog.
Prune with purpose. Keep shrubs open so light reaches the interior and foliage does not mat on the ground. Limb deergrass skirts slightly in late winter so new blades emerge clean.
Check drip at least twice a season. Rodents chew lines on slopes, and stakes can loosen. Replace bitten sections, re pin lines above plant crowns, and balance emitters as plants grow.
Watch and adapt. After each major storm, walk the slope. If you see a new rill starting, scratch in compost and mulch across the line and add a small rock check where water gathered. If a plant failed in an obvious hot spot, replace it with a tougher friend from the same palette.
Where design style meets function
Pasadena’s architecture invites thoughtful planting. Craftsman homes look right with layered greens, textural seed heads, and boulders that peek through. Spanish Colonial facades glow with the silver of white sage and the deep green of toyon. When you plan a landscape renovation for your Pasadena home, let the erosion control planting do double duty as the view from the living room. Low voltage landscape lighting can graze a deergrass clump or up light a toyon trunk, all while keeping fixtures and wiring well clear of mulch. If you add a small entertaining landing above the slope, choose pavers with a porous base rather than slick concrete so runoff drops into your planting instead of charging downhill.
Getting started, without getting overwhelmed
Walk your slope at three times of day. Morning shows dew and shade. Afternoon reveals heat and glare. After a rain shows how water moves. Sketch the zones that behave differently. Pick a palette for each zone, then adjust spacing to your slope. Order plants in trays and 1 gallons when you can, not all 5 gallons. Smaller plants knit in faster, suffer less transplant shock, and are cheaper to replace if one fails. If you prefer to phase the work, tackle the highest risk area first, usually the top third where flows start and where soil loss erodes everything below.
If you want backup on the structural questions, consult a local pro. Crews that design for the Southern California climate will help you avoid the classic pitfalls, from overwatering to mismatched species. And if you need retaining wall design for a Pasadena hillside property, bring in an engineer early so the wall and planting plan support one another.
The right palette, installed with attention and watered wisely, turns a moving hillside into a living, rooted landscape. Your soil stays put. Bees and birds show up. Water bills drop compared to lawn. And when the first big rain of winter pounds the foothills, you can watch the drops disappear into a hillside that holds its shape, year after year.