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After the mound has been raked for basic shape and height, boulders can be placed. Keeping a conservative budget in mind, 100lb to 400lb boulders can be very effective in adding another dimension to the mound, but not be so large as to necessitate the use of costly heavy duty moving equipment. Figure on using 1/2 to 1 ton of boulders for a 12'x25' mound. Keeping in mind that the boulders "average" weight will be about 200 lbs, (some will be 100 lbs others 300-400 lbs), 6 to 10 rocks will be needed. Prices at the local rockery will vary from $100 - $200 per ton, depending on the rock composition. The boulders at Sierra Azul are gray granite which gives a high contrast to the green of the plants and they are the least expensive of the different kinds available locally. For a darker more earth-tone coloration, Sonoma fieldstone or Place fieldstone is popular. Most pickup trucks can handle a ton of boulders and hopefully it will be possible to back up close to the mound to unload, while a sturdy wheelbarrow will easily haul a 200-pound-plus boulder.

Arrange the boulders in an uneven, circular fashion around the perimeter of the mound, some in pairs or groups. Keeping the boulders somewhat to the outside of the mound will show them off, and they will be less likely to be overgrown by larger plants which will be in the interior area of the mound. Make sure depressions are dug before the boulders are set in place. This will make them look more natural than if they are plopped down on top of the soil.

A tip from a landscape contractor friend who is a master rock-scaper, is to align the longest sides or faces of all the boulders in the same parallel plane so they appear as having been uplifted and exposed in nature. Once the boulders are satisfactorily arranged, a second more refined raking and shaping of the mound can be very inspirational, conjuring images and ideas of special plants to use in the spaces and pockets the boulders have created.

Now that the mound has been shaped and raked with the boulders solidly placed, the plants can be chosen and laid out. Small trees, shrubs or tall perennials (4'+), should be placed in the center section of the mound; medium height shrubs and perennials (3-4') in the mid-sections, graduating to lower growing perennials (1-2') and ground covers near the edge. This kind of layout will give the mound a layered or tiered effect, carrying the eye upward to the center of the mound where the taller shrubs and perennials or a small tree will create a focal area. This layout will also help to prevent a larger growing plant variety from obstructing its more compact or lower growing neighbor.


Larger shrubs or small trees to choose from might include: shrubs - Manzanita (Arctostaphylos pajaroensis, A. 'Dr. Hurd', A. 'Sentinel') or Strawberry tree (Arbutus unedo), Toyon (Heteromeles arbutifolia), Wild lilac (Ceanothus 'Concha' or 'Dark Star'); small trees - Arbutus 'Marina', Australian myrtle (Tristaniopsis laurina) or Strawberry tree (Arbutus unedo) trained upright.

Suggestions for mid-section plants are: perennials -Border penstemons (Penstemon xgloxinioides), Autumn sage (Salvia greggii or S. grahamii types), Jerusalem sage (Phlomis), or Euphorbias; shrubs -Rockrose (Cistus), gray or green Santolina, Rosemary, upright forms (Rosmarinus), Lavender, many forms (Lavandula), Australian fuchsia (Correas), and silver foliaged Calocephalus.

Low-growing plants for the outward areas of the mound could include combinations of: Verbenas (hardy forms with several color choices), Erigerons (several varieties of daisy), California fuchsia (Zauschneria), Rosemary, low forms (Rosmarinus), Manzanitas, low forms (Arctostaphylos), and Scaevolas.

Phormiums (color forms of compact New Zealand flax) and ornamental grasses (Stipa, Carex, Festuca, Miscanthus, Pennisetum) add textural interest and work well as contrasting plants near or behind boulders, depending on their size, while different succulents (Echeveria, Sempervivum, Sedum), thymes (lots of varieties) and ornamental oreganos are appealing plants in between and around boulders.

Consideration should be given to the mature size of plants as well as to their year round appeal. Texture and form are as important to a design as flower color, especially as flower color is generally not a constant feature. Perhaps one half of the plants should be chosen for good year round looks while the balance of plants can be selected for seasonal color. Another design consideration is choosing complementary colors of both flowers and foliage, though color clashes in plants are more forgiving than in other situations. Finally, when selecting plants, especially for a small area, be careful not to select a plant "thug" which will overgrow your other plants.

Actual planting of the plants will be easy as the soil has just been turned over. In this worked soil it is not necessary to dig a large hole for the plant, just a little larger than the container is sufficient. If the soil is particularly dry, the hole can be filled with water and allowed to drain before putting the plant in. Plants with tight root balls should have the roots loosened. If it is necessary to cut many roots, the top of the plant should be pruned as well. When filling in soil around the root ball try to eliminate air spaces, these can cause the root ball to dry out even though it is under ground. The soil level around the plant should be kept the same as it was in the container. Newly planted plants should be watered in well to help eliminate small air pockets and establish a water balance between the root ball and the soil. This should be done even when the soil is moist. Plants will need extra water for 4 to 6 weeks to make sure they do not dry out.

During the planting process, the use of redwood soil conditioner, compost or planting mix will encourage faster root growth and greater soil water retention and aeration. A basic granulated fertilizer like ammonium sulfate, cottonseed meal, or 12-12-12, used in small amounts, (1-2 tsp. for smaller plants, 1-2 tbsp. for the larger plants) mixed with the planting soil or used later as a top dress, will insure basic nutrients are provided for initial root and top growth. As deeper rooting occurs, supplemental fertilizer may not be necessary, although once a year broadcast fertilization during the rainy season is a good rule of thumb to keep the plants continually thriving.

An irrigation system for the mound can be as simple as the one at Sierra Azul: light weight, low volume, plastic staked Rain Birds put on the hose end and moved and positioned 2-3 places around the edges of the mound. The plastic Rain Birds are inexpensive, have dial adjusted radius settings, and push into the ground for support. Metal stand supported portable Rain Birds are also available which don't have to be pushed firmly into the soil to stay upright. They are more expensive but should hold up longer.

It is important when using Rain Birds or overhead sprinklers to water deeply and infrequently. At Sierra Azul sprinklers are left for 2-3 hours at each spot. This is done once a month during the summer and early fall and provides adequate water for healthy plant growth. Watering frequency may vary according to soil type, sandy soils requiring more frequent irrigation. Deeper rooted plants will need fewer irrigations than ones that have rooted shallowly. Frequent, shallow watering encourages shallowly rooted plants. This should be avoided in the mediterranean garden.

Drip irrigation is also a simple, effective, and economical way to provide water for plant growth during the summer months. Flexible black plastic, 1/2" drip-tubing can be snaked the long way back and forth on the mound several times and held down with long, heavy wire jute netting staples. Small, 1 gallon per hour, drip emitters are plugged into this main line next to adjacent plants, while extra emitters are added to the main line and 1/8" black plastic spaghetti tube is extended from these in-line emitters in 1 to 3 foot lengths to plants away from the snaked main line. The 1/8" tubing can also be held down with jute netting staples. The drip system can be hooked up to a hose bib with a hose-end fitting or plumbed into the water line before the hose-bib with a separate shut off valve. In either case, a simple, inexpensive, 20 lb in-line pressure regulator and filter should be used at the beginning of the system.

The drip system watering schedule should be approximately 2-3 hours every other week, depending on the drainage of your soil. Sandier soils may require weekly drip irrigations of 1-2 hours until the plants are well established. Again, as with the Rain Bird system, longer and less frequent waterings will encourage deeper rooting and the ultimate need for less water. The drip system is more water conserving than the overhead sprinkler method, but can be more effort to manage if you have a multitude of plants spaced close together. Before installing a drip system, talk to the local sprinkler supply dealer to familiarize yourself with the different fittings and emitters. Keep in mind that the 1 gallon per hour drip emitter is the workhorse of the lot, so try not to be overwhelmed with the wide array of brands of emitters you are likely to see. Half-inch tubing, 1 gallon per hour emitters and 1/8" spaghetti tube should comprise the bulk of the system.

One of the final but most important details to complete the mound project is mulching. To suppress weeds, decrease waterings, and create a finished look, mulch works wonders. Wood chips, shredded bark, leaf mold, or sawdust shavings all work well and are available in bags or bulk. Firewood or tree service companies usually have bulk wood chips available at a reasonable price. Sawdust shavings or shredded bark can be purchased at a landscape supply yard. A 12'x25' mound will need 2-3 yards of mulch for 2-3" deep coverage over the entire mound. A drip system can be covered with mulch for a more aesthetic appearance. The emitters will still function properly under the mulch.

At this point, the Mediterranean mound should be complete. Accent plants or favorite treasures can always be added and existing plants moved as your tastes change. The fall season is an excellent time to plant given that the new rain will provide an ideal kind of watering and encourage strong, deep rooting. This in turn will assure rapid vegetative growth during the warm late winter and spring months, promoting profuse flowering on late winter through early summer flowering plants. Spring and summer planting requires more attention to watering while plants become established, however good plant growth should occur during the warm months.

Plan a trip to Sierra Azul, enjoy our demonstration garden and nursery, talk with the staff, and consider expanding or renovating your garden.

Jeff Rosendale

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