Who hasn't marveled at a dandelion that thrives as it grows from a tiny crack in the pavement? Or more improbably, a tree growing from a rocky outcrop? It makes us stop and reconsider what we know about growth requirements for plants. Many plants are adapted to growing in such extreme environments, and the contrast of soft foliage and flowers with stone leads to interesting and striking results. Crevice gardening allows gardeners to get creative as they showcase beautiful plants in a dramatic setting; it is ideal for someone who is ready for a new gardening adventure.
One advantage of a crevice garden is that it requires only small amounts of water. A variety of plants will work; what they have in common is that they are adapted to thrive in dry conditions, so too much water can lead to deadly bacterial and fungal infections. Another consideration, particularly relevant now, is that this type of garden is more fire safe than a bed mulched with wood chips or bark.
Structure and Site
To create the structure for a crevice garden, flagstones, slate, rocks, or even found materials like slabs of broken concrete are placed like plates in a dish drainer, with the small spaces in between filled with a fast-draining medium. Hypertufa, which is a lightweight do-it-yourself material made from a blend of Portland cement, peat moss, perlite, and water can also be used to make slabs or containers. Because peat is a non-renewal resource, some gardeners use coconut fiber in its place.
As you can see from the illustration, while the roots may reach into the soil below, the surface is rocky and dry, so the garden is not conducive to weeds taking hold (though as we know only too well, weeds are good at growing in even unhospitable environments).
The structure of the garden can be made to simulate a natural-looking rocky outcrop, or it can be strikingly modern or a charmingly whimsical miniature environment. An ideal place could be a small, awkward, overlooked area in your yard that isn't suitable for a traditional garden—maybe a small patch in a side yard, or next to a driveway, or even in place of a retaining wall. Beautiful crevice gardens can also be created in containers—which have the advantage of being able to be moved to a new location according to need—and this is a good option for those with a small yard or just a patio. Wherever the garden is located, good drainage is essential. This can be achieved by planting on slopes, in raised beds, or in containers. Because most plants suitable for crevice gardening are small, raising them closer to eye level makes them easier to see and appreciate. A variety of heights also makes the arrangement more interesting and aesthetically pleasing.
Deeper containers generally work better than shallow ones because they allow moisture to drain quickly from the surface, so the crowns of the plants remain dry while the roots stay moist. You can see how this works with a kitchen sponge. Saturate a rectangular sponge and hold it horizontally until gravity pulls out enough water that it stops dripping, then turn it to a vertical position. You will see that more water easily runs out in the vertical position. Thus, shallow containers tend to retain moisture more evenly throughout the soil than deep ones, though, of course, it is also true that smaller containers dry out more quickly, whatever the shape.
Many plants suitable for crevice gardens grow well in desert climates as well as alpine environments, but in hot climates, it may be necessary to place them on the east side of a building, tree, or shrub to prevent the rocks from getting too hot. Keep in mind that denser, heavier natural stones retain more heat than porous, lightweight material such as volcanic rocks or hypertufa. Placing a patio umbrella where it can shade the plants from the intense afternoon sun can also help prevent overheating. In hot climates, planting in the fall through early spring allows plants to become well-established before the summer heat starts.
Soil and Fertilizer
The most important quality of the soil used for crevice gardening is that it should drain well so that moisture is pulled away from the crown of the plant. The crown is the area most susceptible to attack by pathogens, and it will rot if it is kept moist. The right soil mixture is key, because pores in the soil—the air spaces between the particles of soil—allow the roots to get both the air and the water they need. Soil with smaller pores, such as clay, retains more water than soil with larger pores.
A common mixture used in crevice gardens is 1/3 soil, 1/3 sharp sand (the kind with jagged, irregular shapes), and 1/3 gravel or grit (such as the kind sold for chickens), which gives the plants a mixture of pore sizes. As gravity pulls the water down, the surface will stay dry, but the roots will have the moisture they need. It's important that the roots do not sit in water though; this can be deadly. Because containers dry out more quickly than the ground, a soil that retains a bit more moisture is used in containers.
Another consideration is the pH level of the soil. Most plants—particularly alpine plants—suitable for crevice gardening will thrive in soil that is neutral to slightly acidic, but there are exceptions. Many plants that have evolved in dry steppe or desert climates—including baby's breath (Gypsophila species), candytufts (Iberis species), and saxifrages (Saxifraga)—prefer alkaline conditions. You're stuck with the basic soil in a garden site, but with a small raised bed or a container you can use a soil mixture suitable for the plants you wish to grow. So just as you would group plants with similar water needs together, grouping plants with similar pH preferences together is advisable.
In addition to needing little water, crevice gardens also have the advantage of requiring little to no fertilizer. Too much fertilizer can lead to growth that is too loose and lush, rather than the tight and compact growth that would occur in their natural environments. Container-grown plants do need some fertilizer, since their roots can't reach down into the soil below, but it is best to avoid over fertilizing by applying it at a rate of about half what is recommended on the label.
Plants
Which plants can be grown in a crevice garden? More than you might think. The Denver Botanic Garden's Rock Alpine Garden includes over 3,000 unique types of plants. Their website gives an extensive list of these plants—including their origin and growth requirements—in a very useful searchable database, providing not only valuable information but inspiration for gardeners.
Plants suitable for crevice gardening come from a variety of genera: Cyclamen, Daphne, Dianthus, Draba, Eriogonum, Festuca, Gentiana, Hosta, Iris, Lewisia, Penstemon, Polygala, Primula, Pulsatilla, Saxifrage, Sempervivums, and Tulipa. With some research, you can find which will grow best in your environment. The North American Rock Garden Society has detailed information about suitable plants.
Many of these plants are native to Europe and Asia, but some California natives will work too: bitter root (Lewisia rediviva), Cascade desert parsley (Lomatium martindalei), coyote mint, (Monardella odoratissima), dark throated shooting star (Primula pauciflora), Davidson's penstemon (Penstemon davidsonii), Idaho fescue (Festuca idahoensis,), Sulphur buckwheat (Eriogonum umbellatum), prairie flax (Linum lewisii ), yarrow (Achillea millefolium), and others. Calscape is a wonderful source for information on these native plants.
You might be wondering how to get a plant started in a crevice. Because of the narrow spaces involved, plantings are usually bare root or small rooted cuttings, or plants can be started from seeds. High Country Gardens has additional information on planting.
If you are curious about crevice gardening, remember that you can try it on a small scale without making a major investment in time and energy and still receive strikingly beautiful results. These gardens require little water or fertilizer, and while no garden is maintenance-free, they are low maintenance. The resources listed below can help you get started.
Books:
Tychonievich, Joseph (2016). Rock gardening: Reimagining a classic style. Timber Press.
Seth, Kenton, & Spriggs, Paul (2022). The crevice garden: How to make the perfect home for plants from rocky places. Filbert Press.
Other resources:
Denver Botanic Gardens: Rock Alpine Garden
- Author: Pegi Palmes
Preserving summer flowers, foliage, seed heads, and bracts is a delightfully simple way to accumulate a collection of colorful plant materials from your garden to enjoy throughout the year. Many flowers, seed heads, and some leaves can be preserved by air-drying, often just hung in bunches in a warm, airy room. Leaves gathered when the sap is still rising in the plant, as well as some bracts, can be preserved in a desiccant solution like water and glycerin or silica crystals.
For drying, plant material should be harvested when it is completely free of moisture to avoid the development of mold. If you must gather flowers when they are wet, toss them gently on blotting paper to remove surface water, and stand the stems in a container of water in a warm, dry room until the petals are thoroughly dry. Don't be tempted to start one of the drying processes while the flowers are still damp.
Except for seed heads, it is best to gather flowers for drying early or late in the day; from noon to mid-day the plant is at its most vulnerable and more inclined to wilt than respond to the drying treatment. Gather the flowers at the mid-way stage of their development, or just before they are fully opened. An exception to this rule would be everlastings like statice and strawflowers, which can be harvested when they are in full bloom.
Air drying is the simplest method of preserving plant materials. The process is not an exact science and the actual temperature is not critical, though it should not fall below 50°F. A dry area with no direct sunlight and a small oscillating fan set on low is ideal. Some plant types are best dried upright with the stems loosely held in tall containers and the heads fanning out wide and away from each other. Hydrangea heads and gypsophila are two of the plant materials which can be air dried with their stems standing in a little water. As the stems gradually absorb the water it evaporates and eventually, over a week or so, the plant material dries more or less naturally. Other flowers and foliage may be dried horizontally spread out on racks or shelves covered with absorbent paper. Some plant materials do well hung upside down by their stems. Tie the materials into small bunches, with larger stems tied individually.
Desiccant options available are alum powder (aluminum sulfate) and household borax, both of which are suitable for small, delicate flowers. Silica gel absorbs the moisture from the petals. The blue beads change color from blue to pink once the gel is saturated and needs to be replaced. Desiccants are available at craft and hobby stores. For drying with a desiccant, spread a thin layer in a container, arrange the plant material by type and not touching, then cover them with the desiccant until it forms a top layer about ½ inch above the plant material. Use an airtight tin and set it aside for 2 to 5 days or speed up the process by drying the plant materials in an oven set at the lowest temperature, using an ovenproof dish without a cover, keeping the oven door slightly ajar.
The fastest method is in the microwave. Layer the material in a microwave-proof container without a lid. Process on low power. Since drying times will vary according to the power of your microwave, the type of container used, and the density and moisture content of the plant material, it is best to experiment; check progress every minute or so and make notes of the processing time. Glycerin is another preserving method. The plant material absorbs the glycerin, replacing water content with glycerin, keeping flowers supple and bright. Simply place the stems of fresh flowers in a mixture of two parts lukewarm water to one-part glycerin. Let the flowers sit in the mixture for two to three weeks. Some plant materials will undergo slight color changes with this process.
Whatever method you choose, you could have beautiful plant materials to enjoy throughout the year
There are no walls or fences surrounding the two-acre Ripon Community Garden located smack-dab in the middle of a local Ripon residential neighborhood. But the garden has become a beloved community landmark since its beginnings in 2016.
The non-profit garden includes 92 4' x 10' wooden garden boxes. Seventy-five boxes are available to rent for $40 per year to folks (refundable to the gardener upon departure from the garden) to grow their own fresh fruits, veggies, and flowers to their hearts desire. Twelve boxes are harvested to provide fresh produce for the Ripon Senior Center and Bethany Homes, and four boxes for the “Sprouts” children garden, maintained by the local Girl Scout Troop.
Each garden bed has its own irrigation system. They can be tended by one person while others may have several gardeners working together. Children and their parents share some garden beds as well.
Gardeners include those new to growing produce as well as seasoned gardeners who grow their favorite tomatoes, herbs, fruits and veggies, as well as flowers.
The garden site includes an enclosed chicken coop for its egg-laying chickens. The chicken coop is a delight to many “city” children who may have never seen chickens.
Joan Graham, a former garden box holder, took over the garden's operation a few years ago and loves being outdoors, helping gardeners and their many different types of produce, flowers, and herbs grown in their gardens. Joan keeps a “waiting list” for those interested in renting a garden box.
She gets a helping hand from Karen Talbot, Harvest Coordinator, who oversees harvesting produce from the cherry, nectarine, aprium (a cross between apricots and plums), lemon, and lime trees. She also helps during planting season. Karen also heads the Harvest Team, cleaning boxes after the harvest, and once a gardener vacates a garden box.
The garden also includes fruit trees such as peaches, persimmons (both Fuyu and Hachiya). The harvested produce is available to box holders or others. According to Joan, the garden is unable to charge for the garden grown produce unless it sold as a fundraiser.
There is “plenty of support” for the Ripon Community Garden from various local businesses and organizations, said Joan, from financial donations, as well as in-kind donations such as seeds and discounts on needed garden tools and items. Even the local Boy Scout Troop has found the Ripon Community Garden a great place to volunteer.
Board Vice President Penny Hansen produces a monthly newsletter for box holders and it posted on the garden bulletin board for visitors to read.
The garden is open daily for the community to visit and enjoy. Visitors can walk through the garden (please no picking of produce), enjoy the shade under the pergola, have lunch on one of the picnic tables, and appreciate the serenity, peace, and beauty of the garden.
- Author: Cheryl Carmichael
Serotiny, n, (Botany)
In botany, serotiny means “following” or “later.”
Serotinous leaves follow flowering on plants: ex. redbud trees leaf out after the flowers on the branches fade.
Serontinous flowers follow the growth of leaves forming serotinous fruit (cones) that release their seeds over an extended period of time or only in the face of environmental triggers. In California, South Africa, and Australia, plants with serotinous fruit include many species of pines, all cypress and sequoia, some spruce, and eucalyptus.
In California, serotinous fruit is an ecological adaptation to regular wildfires. The “fruit” are the cones held high in the canopies of needled trees that can exist for years as sealed containers until bursting open and dispersing seed. These seeds are held in cones by a resin that coats the outside of the cone and glues the “petals” of the cone together. The heat of fire will melt the resin, unfolding the petals and releasing the tiny seeds. The germination of these seeds following fire replenishes the forest with new plant material. The science of “Fire” as an environmental trigger event is called pyriscence, is used synonymously with serotiny and is the most studied case of trigger events.
Other potential trigger events include death of the parent plant or branch, wetting or too much water, excessive sun exposure, drying atmosphere, and fire followed by very wet conditions.
Plants that have leaves and flowers at the same time and drop seeds at maturity during a
growing season are termed coetaneous.
EXAMPLES: CLOSED and OPEN CONES
Aren't native plants supposed to survive on rainfall? Should I water them during the summer? If so, how much?
The answer depends on which plants are living in a particular site. Is the soil loamy, sandy, or heavy clay? What is the sun exposure? The high and low temperatures? How well-established are the plants?
Observing how native plants grow and thrive in the wild is instructive and can guide best practices for home gardeners to use. Note which plants thrive in sunny locations, or near water, or in rocky outcrops. In this photo, it's easy to tell the north-facing from the south-facing slopes.
Watering:
Because most California soil is dry during the summer, many native plants are well-adapted to those conditions and won't tolerate standing water. This is particularly an issue with clay soils that don't drain well. The excess water can cause roots to rot, or it can cause suffocation as the water prevents oxygen from getting to the roots. Watering an established native—meaning one that is 1-2 years old and has at least doubled in size—even just once a month during the height of summer can be enough to kill it.
This is also because California natives, and many other plants, rely on mycorrhizal fungi that live symbiotically in the roots of the host plant. These amazing fungi provide critical micronutrients and increase the absorptive capabilities of the plant's roots by up to one thousand times in exchange for the carbon provided by the host plant. Mycorrhizae even secrete chemicals that help to suppress weeds! However, the bacterial and fungal pathogens that can kill mycorrhizae thrive in warm, moist conditions, so too much watering in hot weather can be deadly for them.
In nature, plants with deep roots—such as oak trees—pull moisture from the water table and share it with other nearby plants. Roots will grow in the direction of a water source, and it is surprising how wide mature root systems are. Many have a root system three times the width of the crown. This illustration shows how the process works.
Knowing this, home gardeners can mimic nature by creating a bioswale, trough, or catch basin that collects water and allows it to be transferred to nearby plants. A garden designed with riparian plants inside a naturally moist or well-watered area with drought tolerant plants nearby takes advantage of this. Local riparian plants include trees such as Acer negundo (box elder), Cornus sericia (creek dogwood), Fraxinus latifolia (Oregon ash), and Salix gooddingii (San Joaquin willow). Riparian perennials and shrubs include Rosa californica (California wildrose), Vitis californica (California grape), and Erythranthe guttata (seep monkey flower). Calscape provides more examples and gives the general water requirements for California natives. WUCOLS IV (Water Use Classification of Landscape Species) is another very useful website for determining the specific water needs of thousands of plants.
Although they may go through a period of dormancy and survive without summer water, most native plants look better with judicious supplemental water. Another consideration is that extremely dry plants pose a fire danger. Some gardeners aim to shorten the period of summer dormancy by extending the watering period in the spring and fall. But it is important not to waste water by overwatering plants, particularly during drought conditions.
This may translate to watering young plants every week or two and established plants once a month. In general, established native plants should be watered deeply but infrequently enough to allow the soil to dry out in between watering. The top few inches should remain dry around small plants, deeper with mature plants. To water deeply, it is necessary to water slowly, allowing the water to soak in. If a heat wave is predicted, water before—rather than during—the worst of the heat. Watering early in the morning on a relatively cool day is best. Rinsing the dust off the leaves occasionally also helps plants look their best.
If drip irrigation is used, move the water source farther from the center of the plant as it grows. It is best to have several emitters per plant, placed at the plant's drip line. A single drip emitter near the crown encourages a small root ball and makes the plant more susceptible to rot and diseases.
Overhead sprinklers do not work well with most non-riparian native plants. A light watering that simulates a summer storm early in the morning will probably not harm the plants, but anything placed close to a sprinkler head will probably get too much water. Light hose watering is a preferable way to water, but not directly on the crown of the plant. It's better to spray the water around the drip line, a few feet away from the root ball.
Whatever method is used, it is important to check the soil before watering rather than to keep to a schedule. If the soil is moist at the root level—checked with a moisture meter or simply by poking a finger into the soil—it is not time to water, even if the surface appears dry. When in doubt, do not water! But continue to monitor the plant, especially if newly planted. Wilting leaves are not necessarily a sign that water is needed; confusingly, they can also indicate root rot caused by too much water.
Mulching:
Gardeners can take a cue from nature again regarding mulch. Many native plants create their own mulch with leaf litter. This type of mulch tends to be light and airy, allowing for good airflow. It doesn't wick moisture up from the soil, but still shades the roots, suppresses weeds, and helps maintain soil moisture and temperature. It also improves soil as it decomposes. So leaving leaves in place is a good practice, whenever possible.
Some natives, particularly desert and prairie plants, do well with gravel or rocks as mulch. Wood chips or bark work well with most other others, and shredded redwood bark is best for coastal and Sierra natives. Many do well with a large rock placed nearby.
Mulch should be 2-3” thick and kept away from the trunks or stems of plants. Ideally it is applied in the spring or fall, but more can be added in the summer if it is too thin, for all the benefits mentioned above.
Deadheading and Pruning:
Many native plants—including Monardella villosa (coyote mint), Verbena lilacina (lilac verbena), Mimulus spp. (monkeyflowers), Penstemon spp. (penstemon), Eschscholzia californica (poppies), and Salvia spp. (sages)—respond well to deadheading with new blooms, though some gardeners choose to leave the seeds for reseeding or for their value to wildlife.
Summer is a good time to tip pinch shrubs if you want to encourage denser growth. It is also a good time to thin or prune shrubs and trees, if necessary. Native evergreen trees are susceptible to disease if they are pruned in wet weather, so summer is a better time to prune them. Because requirements vary with different plants, it is best to check for reliable information on specific plants before pruning them and to use the services of a qualified arborist for pruning large trees.
Takeaways:
- Mimicking nature as much as possible with plant placement, watering, and mulching is a good way to be successful with California native plants.
- Checking the moisture level at the root ball is important. Allow the top few inches of soil to dry out between waterings.
- Watering deeply and infrequently is recommended for most non-riparian natives, but watering needs vary with environmental conditions and the age of the plant.
- Take advantage of resources such as Calscape and WUCOLS IV for detailed information on thousands of plants.
- Many native plants respond well to deadheading, tip pinching, and pruning during the summer; look at the requirements for specific plants.
For more information:
Bornstein, C., Fross, D., and O'Brien, B. (2005). California Native plants for the garden. Cachuma Press.
California Native Plant Society: Mulching basics. https://www.cnps.org/gardening/prepping-and-planting/mulching-basics
California Native Plant Society: Watering California native plants https://www.cnps.org/gardening/prepping-and-planting/watering
Calscape California Native Plant Gardening Guide. https://calscape.org/planting-guide.php
Las Pilitas Nursery: How to plant California native and other drought tolerant plants. https://www.laspilitas.com/planting.htm
Popper, H. (2012). California native gardening: a month-by-month guide. University of California Press.
