You may find yourself digging a planting hole, filling it with water, then turning to the next job of adding amendments to the soil you’ve removed. An hour later you realize the hole is still full of water; even a day later the water’s only down an inch.
Most plants won’t live long in waterlogged soil. Even if they can stand the airless condition, they won’t be able to tolerate the salts that build up from evaporation. What are your alternatives? You can build raised beds for your plants or simply use container plants (the only solution if your garden lies over solid rock). You may also be able to improve soil drainage if the problem is caused by a layer of hardpan or clay just below the surface, or if the soil is compacted.
TRY TO DIG TO A POROUS LAYER
Your soil may contain a shallow layer of hard or dense soil just under the surface, but the layers below may be porous. To test your soil consistency, use a posthole digger to dig down 2 ¼ or 3 feet; check for a change in color and consistency. Also fill the hole with water to check drainage. If the water drains away in a relatively short time, this approach will work. (If you need to dig several holes, you may want to consider renting power equipment.)
Fill the hole a quarter of the depth with fine sand or sand and peat moss (this fine-grained material will help draw water downward). Set the plant in the hole so the joint between roots and trunk—called the “crown—is higher than the surrounding soil. The crown is sensitive and should be in dry, airy soil, or even left uncovered.
Roughen up the sides of the planting hole so the roots can penetrate more easily as they grow. Add organic amendment to the soil you removed until a third to a half of the mix is amendment. If needed, add nitrogen, and blend in bone meal or superphosphate following package directions. And if your soil tends to be alkaline or you want to guard against chlorosis, add sulfur and iron chelate.
If there isn’t much topsoil over the hard under-layer, make oversized planting holes. Filled with improved soil, these holes act like giant containers. The roots will never be able to penetrate the surrounding unimproved soil, so the holes have to be big enough for the roots to mature and support the top growth. Here are suggested dimensions:
Large tree—6 feet wide by 3 feet deep
Small tree—5 feet wide by 3 feet deep
Large shrub—4 feet wide by 3 feet deep
Small shrub—2 feet wide by 2 feet deep
Flowers—plant in 18-inch-depth of improved soil
WHEN YOU CAN’T BREAK THROUGH
If the planting site is on high ground, dig a sloping ditch toward a driveway, street, or downslope. Place terra cotta or composition drain tiles into the planting hole, covering the joints with tar paper. Cover the entire drain with crushed rock and then with part of the amended soil you’ll use to fill the planting hole.If the ground is level, digging a sump hole is the only solution for getting water to drain. Dig a hole 3 to 4 feet wide and 4 to 5 feet deep right at the planting site or about a foot to one side. Add a 1-foot layer of fine sand and cover with fiberglass. If the sump hole is to one side, lay a piece of drain pipe from the planting hole to the sump, inclining it sharply downward from the planting hole into the sand. Then refill the sump hole. A sump hole usually is not a permanent solution, since silt will eventually fill it and make it useless; however, there is the chance that the plant roots may have broken their way into the hardpan by then and improved drainage by themselves.In impermeable soil, you must set the plants a little above ground level to keep the crown in dry, airy soil. To keep above-surface soil in place, circle the plant with a low edging board.
MAJOR SURGERY FOR COMPACTED SOIL
Solid layers of soil that were compacted by bulldozers can be improved if you can put off your landscaping plans for a while and enlist the help of a landscape contractor who has heavy duty equipment. The soil must be cultivated to a depth of 18 inches or deeper. You then plant annual rye grass. The root system of rye grass is deep and wide and will break up compacted soil at a deeper level than you could reach with plowing. Keep the grass growing for 6 months to a year with regular watering. During this time, cut the grass once or twice, leaving the cuttings where they fall. Clipping the grass keeps it from going to seed and dying too soon.
When the grass is 6 to 10 months old, the landscape architect will have his men plow in the grass to a depth of 9 to 12 inches and add an organic amendment and any necessary nitrogen. You can then dig planting holes and set in your plants. Where possible, leave half the root ball above the natural surface and mound good soil around it. Cover the area around the plant with a two- inch layer of organic material. It will hold in moisture and you’ll have to water less frequently. Once a year, spade the mulch into the soil and replace it with a new layer.
PLANTS FOR SOGGY SOIL
You may find the impermeable layer of soil just under the surface too thick to penetrate. The solution to this problem is to install a drainage system. Some plants withstand the wet soil caused by bad drainage better than others. On the opposite page you’ll find a listing of the plants that do the best job of tolerating wetness.
TREES
Quince (Cydonici oblongaJ. Deciduous tree with 2-inch flowers, edible fruit.Red maple (Acer rubrum). Deciduous. For cool or coastal areas.Sweet gum (Liquidambor styrciciflua). Fall color, interesting seed pods.
Sycamore (Platcinus). Messy fluff from seeds. Deciduous.
White alder (Alnus rhombifolio). Deciduous western native that may reach 90 feet.
Willow (Salix). Cuttings root quickly. Many shapes and sizes from weeping to shrubby.
SHRUBS
Oleander (Nerium oleander). Best in warm climates. Flower colors pink, white, yellow.
Pampas grass (Cortaderia selloana). Big grassy clumps produce feathery white plumes.
Privet (Ligustrum). Classic hedge plant, but can be small tree. Most are deciduous, some are evergreen.
BULBS
Iris. Beardless and Louisiana iris have flowers in white, yellow, pink, red, purple, many blues. Japanese iris blooms in July. Siberian iris has butterfly flowers on 2 to 3-foot stems.
ANNUALS
Calendula. Winter-blooming in mild areas. Flowers in orange and yellow.Monkey flower (Mimulus tigrinus). Sprawling growth to 1 foot. Blooms spring and summer.
VINES
Cup-of-gold vine (Solandra guttata). Salt-tolerant evergreen with big, trumpet-shaped yellow flowers.
Hall’s Japanese honeysuckle (Lonicera japonica Halliana). Evergreen in warm climates. Strong perfume.
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Tim Lundie, Editor
