Gardens with Alkaline Soil

Slightly alkaline soil is the perfect home for some plants, but too much of a good thing can be detrimental to the health of many garden plants. One of the side effects of arid regions where rainfall is scant is alkaline soil with a high pH rating, but with attention and care, you can modify garden beds to lower the pH. Or you can choose plants that thrive in alkaline soil. Fortunately, here you'll find many low-maintenance, well-adapted performers that fill the bill.

If you need a ground-cover for shade where ample water is available, consider adaptable burgundy-leaved bugleweed or lustrous green-leaved pachysandra. Trumpet vine and Japanese wisteria are alkaline-tolerant vines that will happily scramble over a rustic fence or arbor.

Many shrubs are also adaptable. Doublefile viburnum, for example, is no less beautiful when grown in slightly alkaline soil than when it's rooted in slightly acid soil. Rather than amending your entire property, you can cut your workload considerably by grouping together foliage and flowering plants that prefer alkaline soil, such as lilac, peony, gypsophila, pincushion flower, and sun rose.

Save the work of amending garden soil to lower the pH for those beds destined to host annuals or perennials that need neutral or slightly acidic conditions. Or, consider growing those plants in containers filled with their favorite soil mix.

Acidifying Alkaline Soil

Lowering the pH of alkaline soil is time consuming, and it's impossible to permanently "fix" alkaline soil in one fell swoop. The most direct way to lower the pH of alkaline soil is to amend it with garden sulfur, which should be thoroughly mixed into the soil. Use caution, however, and apply only a small amount at a time. Soil sulfur is potent. About 1 pound (0.45 kg) per 100 sq ft (9.3m) will noticeably lower the pH, usually by 0.5 point on the pH scale, but you will need to wait 8 weeks before making another application. Even when it is thoroughly mixed in, using too much soil sulfur in one application will form pockets of strong acid in the soil that can burn plant roots, undoing all the good you are trying to do.

In combination with soil sulfur, work acidic soil amendments, such as peat moss, oak leaves, leaf mold, or rotted sawdust, into the soil. In addition to lowering the pH, these soil amendments will improve the soil's texture and help it to retain moisture, which is usually a pressing issue where alkaline soils reign.

To compound the problem of altering soil pH, the water, too, is often alkaline in areas where the soil has a high pH. As a result, the alkaline tendencies of the soil are reinforced each time you irrigate, using a garden hose and municipal water. You can help to offset the process by using fertilizers that are intended for acid-loving plants, in addition to making liberal use of organic matter and soil sulfur. Consider hooking up your house gutters to barrels and collecting rainwater, which is naturally soft, for use on special collections of acid-loving plants.

Amazing Annuals

Annual flowering plants grow for only one season and are often surprisingly adaptable to soil pH, so they are ideal plants for gardens with alkaline soil. Make the most of annuals by combining them according to time-honored garden design principles. Grow plants with a diversity of flower shapes and plant habits. Set rounded mounds of butter daisies alongside the upright flower plumes of celosia, for example. Add instant height to an annual bed by incorporating trellises for annual vines, such as scarlet runner bean, to climb. This is a design trick that adds the illusion of permanence to your garden design. And, underneath it all, grow evergreen ground-covers like licorice plant, or evergreen perennial ground-covers that can tolerate alkaline soil, such as bugleweed and pachysandra.

The beauty of annuals, for gardeners with alkaline soil, lies not only in their strong flowering performance but also in the fact that they bow out completely when their growing season is finished. This allows you to apply a fresh application of soil sulfur and to turn under old mulch to enrich the soil in beds with organic matter each fall when the bed is cleared of debris. Lay down a winter mulch of large bark chips, evergreen bough, pine straw, or some other mulch that won't blow away, to protect the soil from erosion, readying it for planting first thing in spring. Beds dedicated to annuals can become a movable feast, allowing you to experiment with new plants in new combinations each season.

The Container Alternative

Rather than fight the terrible twosome of constant dryness and alkaline soil that can be found in many areas, and even along lime-rich concrete foundations, driveways, and sidewalks, many gardeners color up their summer gardens with container gardens grown in neutral to slightly acid soil. Commercial potting soils are usually slightly acidic, and they can be amended, if necessary, with additional peat moss or organic material for growing hydrangeas, camellias, or other acid-loving plants.