- 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
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.
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.
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.
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.
Denver Botanic Gardens: Rock Alpine Garden