Cover Ground With Ground Cover

Trailing rosemary eventually gets somewhat deep.

Within the outdoor rooms of home gardens, shade trees are ceilings, shrubs and hedges are walls, and turf and ground cover plants are floors. That is why the selection of plants for such purposes is as important as the selection of paint and carpet for indoors. Among ground cover plants, durable turf grasses for lawns are the most common and functional.

There are so many more types of ground cover plants besides turf grasses though. A few of the lower, denser and more resilient types of ground cover plants can function as turf if necessary. Many more function as mulch to control erosion, contain dust or conceal mud. Many inhibit proliferation of weeds. Some retain a bit more moisture than they consume.

Appropriate ground cover plants most definitely have many advantages. They also have certain disadvantages. Although most require less maintenance than the weeds that they exclude, they require more maintenance than simple mulch. Also, most require irrigation. They might be trailing perennials, sprawling shrubbery, or unsupported wandering vines.

Trailing gazania, Hottentot fig (freeway ‘ice plant’) and various ice plants are some of the more popular perennial ground cover plants. They and others migrate by trailing stolons or rhizomes. They are among the lower and more compact types of ground cover plants. Some need no more pruning than edging. Many propagate easily by division or cuttings.

Sprawling sorts of juniper, ceanothus, cotoneaster, myoporum and rosemary are shrubby ground cover plants. They get significantly deeper than perennial plants, and some sorts can eventually get too overgrown to be practical. Rosemary, myoporum and cotoneaster are conducive to shearing as they mature. Ceanothus and juniper need significant area.

English ivy, Algerian ivy and star jasmine are vining ground cover plants that should stay rather low if properly maintained. However, they can climb into shrubbery and trees, and even buildings. The ivies are famously aggressive, and spread indefinitely by rooting as they migrate. Severe pruning can renovate some overgrown vining ground cover plants. Bougainville gets rather shrubby and deep, even without support.

Licorice Plant

Licorice plant can become vegetative mulch.

This is not the genuine licorice of confectionery. This more popular home garden licorice plant, Helichrysum petiolare, is more of an ornamental plant than a culinary herb. Its mild foliar aroma resembles that of genuine licorice, but is very faint. Without disruption of the foliage, the aroma is imperceptible. Since the foliage can be toxic, the flavor is irrelevant.

Licorice plant is popular for its appealingly silvery foliage. Some cultivars are variegated. ‘Limelight’ is strikingly pale silvery chartreuse. The small, rounded and evergreen leaves are distinctly tomentous (slightly fuzzy). The sprawling stems tend to disperse over older growth, and might get deeper than a foot and a half. Mature plants get wider than six feet.

Licorice plant is susceptible to extremes of temperatures. Within more severe climates, it appreciates a bit of partial shade during excessively warm and arid weather. Foliage can roast from harsh exposure. Where winters are cool, foliage appreciates shelter from frost. Roots are susceptible to rot with excessively frequent watering, or inadequate drainage.

Mulch Retains Moisture And Insulates

Mulch helps to insulate the soil.

Nature is smart. It should be. It has been operating efficiently since the beginning of time. That is certainly longer than anyone has been gardening in defiance of nature. Imported plants that need unnatural watering and soil amendment continue to benefit from nature. Some assets, such as weather, are direct from nature. Some, such as mulch, are copied.

Summers are long, dry and somewhat warm here. Without rain, there is plenty of time for the soil that roots inhabit to become dry. Warmth and aridity increase the consumption of moisture by plant species that are not accustomed to such extensively dry weather. That is precisely why landscapes and home gardens are so reliant on supplemental irrigation.

Because water is expensive, plants that do not require much of it are popular. Automated irrigation systems should operate as efficiently as possible to minimize waste. Since turf grass is very consumptive, lawns should not be overly expansive. Conservation of water is common here. There are several techniques for doing so. Mulch is one of the simplest.

Although adding mulch to a garden is unnatural, it works like the natural detritus within a forest. It retains moisture and insulates the surface of the soil. Without mulch, surface soil can become uncomfortably dry and warm for roots. Mulch also inhibits the proliferation of weeds. Because weeds consume moisture, their absence indirectly conserves moisture.

Mulch generally goes into the garden during early spring, before weed seed germinates, and after the removal of the detritus of winter. It can be practical at any time though, even as the soil becomes dry and dusty through summer. Various forms of mulch are available from garden centers. Home compost works splendidly, but costs nothing more than labor.

Alternatively, several types of groundcover can function as mulch. Some types consume more moisture than they conserve, but exclude weeds. Some types, such as ceanothus, lantana and licorice plant, might not crave any more water than the plants they surround. Their maintenance should involve less effort than removal of weeds which they displace. They are more visually appealing anyway.

Mulch Is Lowly But Practical

Mulch is less interesting than useful.

Gardening is unnatural. Most popular plant species are not naturally native. Cultivars are products of unnatural selection and breeding. Most plants like unnatural watering. Some enjoy unnatural fertilizers. Removal of their detritus is unnatural. So is the replacement of their detritus with mulch. Actually, most of what happens in the garden is quite unnatural. 

Ironically, gardening is how many of us incorporate more nature into our lifestyles. Much of our effort compensates for what plants naturally crave but unnaturally lack. Watering is necessary for plants that get rain through summer within their natural ecosystems. Mulch might be nice for plants that naturally benefit from the decomposition of their own debris.

In nature, most plants benefit from their own debris. They enjoy the nutritiously decaying organic matter and enhanced moisture retention. Their shallow roots enjoy the insulating effect on the surface of the soil. Debris of some plants excludes other competitive plants. Mulch is not a perfect substitute for such detritus, but partly compensates for its removal.

Although it would likely be an asset to the plants that produce it, the detritus produced by most plants can not stay in the garden. Much of it is too abundant. Some is too shabby or too coarsely textured. Some might become combustible as it accumulates. Diseases can overwinter in some types of debris. Mulch is more sanitary, neater and less combustible.

Most mulches are organic matter of one sort or another. Compost does not last long as a mulch, but is appreciated by most plants. Uncomposted chips from a tree service occupy nitrogen as they decompose, but are more effective for inhibiting weed growth. Products that are available as mulch at garden centers are more refined, but also more expensive. 

Some dense ground cover plants perform something like mulches. Many consume more moisture than they retain though. Also, they can retain bits of potentially infectious debris that falls from diseased plants above. Nonetheless, they insulate the surface of their soil, and inhibit or exclude weeds. Gravel over ground cloth is inert, but requires no watering.

Much Ado About Mulch

Not many weeds get through mulch.

Mulch was not invented by humans. Most plants make some sort of mulch naturally. Even desert plants that live on bare ground shed foliage that decomposes to be recycled back into the soil, and provide nutrients for the roots below. Redwood, most pines and most eucalyptus are extreme mulchers that generate thick layers of foliar debris that benefit their own roots, but inhibit the growth of competing trees. Knotweed, Hottentot fig (freeway iceplant), ivy (both Algerian and English) and other dense groundcovers are their own mulch, and also work well for substantial plants that grow amongst them.

There are a few advantages to mulch. Although ground cover mulches consume some degree of moisture, mulches benefit plants by retaining moisture at the surface of the soil. Mulches also insulate the soil, so that it is more comfortable for roots that want to be near the surface. Most weed seeds that get covered by thick mulch can not germinate and emerge through it. Those that try to germinate on top probably can not get their roots through to the soil below. Besides, mulch simply looks better than bare soil.

Mulch is generally spread in early spring, before weed seeds are completely germinated, and while the soil is still damp. However, moisture retention is still a concern through the warm and dry weather of summer. A thin layer of finely textured mulch added over thinning groundcovers (without completely burying the foliage) can rejuvenate tired old stems by giving them something more to root into. This works well for knotweed, English ivy and even trailing gazanias.

Mulches should generally be well composted so that they do not take too many nutrients out of the soil for their own decomposition. However, uncomposted coarse wood chips, like those often recycled from tree services, are even more effective at controlling weeds while fresh, and they tend to decompose before they become a bother to larger plants.

Small volumes of mulch can be purchased in bales at nurseries and garden centers. Composted redwood soil conditioner is a popular soil amendment that can alternatively be a nice finely textured mulch to spread thinly over small areas or in planters. Larger volumes of more coarsely textured and less expensive mulching materials can be obtained by the yard from garden supply stores.

Plants To Cover New Ground

Ground cover plants are quite variable.

Lawn is both the most common and the most horticulturally incorrect of landscape features. Not many landscapes lack lawn. After all, it is the most useful part. Yet, with few exceptions, it requires more water and maintenance than anything else, and in most situations, than everything else combined!

Other groundcover plants are not nearly so greedy. Some need only occasional attentions. Most want less water, and some need very little water or none at all once established. No other groundcover functions like lawn. However, they each have particular advantages.

Ideally, groundcover plants do more than just look good. Most cover otherwise exposed soil so that weeds or other unwanted plants do not dominate. Some groundcovers help to stabilize soil. A few even work as living mulch so that soil does not stay too harshly exposed for other plants to be comfortable in it.

Low growing shrubbery, like creeping ceanothus and some types of juniper, can get too deep and unmanageable for confined areas. They tend to work better where they have room to spread outward uninterrupted. Otherwise, the edges can get quite shabby if they need to be pruned back for confinement. Some sprawling cotoneasters tolerate pruning better, both on top and the edges.

Coarse vines, like honeysuckle, naturally stay low where they have nothing to climb, although they need occasional pruning to stay tidy and confined. High branched trees, like most types of eucalyptus, are beyond the reach of busy tendrils or twining vines. However, Algerian and English ivies, although considerably tidier and uniform, can cling directly to the trunk of any tree to become a wicked mess out of reach!

Old fashioned Hottentot fig (freeway iceplant) can be aggressive where it needs to be pruned around the edges, but is actually quite complaisant otherwise. It does not pile up too deeply because older stems decay as readily as they get overwhelmed by new growth above. Vigorous growth is an advantage for filling in quickly, and subduing weeds. ‘Real’ iceplants are smaller, more docile around the edges, and much more colorful when they bloom.

Leaf Litter Is Perfectly Natural

Mulch merely substitutes for leaf litter.

Forests lack gardeners. In the wild, there is no one to rake fallen leaves or blow them away. Foliage falls from trees and onto the ground, where it stays as it decomposes. It is the natural process. Raking and blowing leaf litter away is unnatural. It deprives the soil and organisms that inhabit it of significant organic matter that they crave. It also interferes with insulation and moisture retention.

Of course, there are some natural processes that are not so desirable in home gardens. After all, that is why raking and blowing is standard procedure. It is not practical to leave leaf litter on lawn, ground cover, pavement or roofs. Raking and blowing removes leaf litter from where it is unwanted, or at least moves it to where it is less visible. Leaf litter seems to be so useless and unwanted.

However, other procedures are necessary to compensate for the lack of leaf litter. Mulching insulates soil, retains soil moisture, and inhibits weed growth. Watering adjusts to deficient moisture in exposed soil. Weeding eliminates weeds that germinate and grow where there is nothing to inhibit them from doing so. Herbicide may be more practical. It is all so contrary to natural processes.

It is somewhat obvious why deciduous plants defoliate through autumn and winter. They do not need their foliage as much while days are shorter and sunlight is less intense. Also, they do not want to be battered by winter wind, or collect heavy snow. Yet, their desire to mulch their own soil is not so obvious. Evergreen plants do it also. They just do it slower, and generally throughout the year.

In fact, many evergreen plants are more efficient with their mulch than most deciduous plants are. Leaf litter of eucalypti, camphor, bay and nearly all conifers actually has a preemergent herbicidal effect. It inhibits germination of seed that can reach the soil. It can be a disadvantage for wildflowers, or an advantage for weed control. Incidentally, coniferous leaf litter is likely to be combustible.

Leaf litter, composted or left to its natural processes, is natural.

Two Birds With Many Stones

Gravel and stone function like mulch.

Fads are not necessarily bad ideas. Some evolve out of good ideas. Others are recycled old ideas that worked. The current popularity of stone, gravel and artificial ‘dry creek beds’ is probably the result of the drought. Yet, they were becoming popular before the drought. This is not their first time around either. They were popular through the 1970s and the 1950s as well.

Stone and gravel obviously do not need to be watered. Therefore, more area occupied by stone, gravel or dry creek beds equates to less area occupied by plants that want water. Such areas are not as useful as pavement or decking, but are more appealing where space does not need to be useful, and work nicely where the ground it sloped too much for pavement.

Stone around the trunks of mature trees works like an insulating mulch so that lawn grass and groundcover plants can be kept at a safe distance. Otherwise, the water needed to sustain the grass or plants against trunks can cause root or trunk rot. However, stone should not be piled so deeply that it holds moisture or interferes with aeration.

Stone is actually better than mulch in some situations. It does not decay. Stones and larger gravel are not likely to be blown or raked away, although small gravel can be difficult to separate from debris while raking. Since stone does not need to be replenished, groundcloth can be installed beneath it to prevent weeds from growing through.

Artificial dry creek beds do not need to be completely dry all the time. They can actually improve drainage in low spots that get saturated during rain. Stone on groundcloth drains better than soil or plants do. Artificial creek beds that are only ornamental should stay in low spots anyway. They look even more unnatural in high spots that water would not naturally drain to.

A few plants can go a long way in larger areas of stone or gravel, and particularly in artificial dry creek beds. If the stone is done properly and is appealing enough, the plants merely add a bit of color, form and texture, without completely obscuring the stone. Drought tolerant plants are of course more appropriate if the intention of stone is to conserve water.

Mulch Is Imitation Of Nature

91113thumbEvery living thing in our gardens came from the wild somewhere. A few plants might be natives trying to adapt to synthetic landscapes. Some might be from similar climates. Some are likely from very different climates. Even houseplants came from the wild somewhere in the World. Regardless of their respective origins, in home gardens, all plants want to behave as they would in the wild.

Many plants want to defoliate at this time of year. Even some evergreens want to shed some of their old foliage before winter. Some perennials die back to the ground. Most summer annuals are already dead. There is an abundance of deteriorating organic material getting discarded by the plants that produce it. In the wild, all this detritus would naturally fall to the ground and decompose.

That might be a problem in parts of our refined landscapes. Fallen leaves must be raked from lawns, decks, pavement and various other flat spaces outside. If left too long, they shade out lawns, ground cover and bedding plans. Fallen leaves can stain decking and pavement too. The worst diseases of roses and fruit trees overwinter in fallen infected debris that does not get raked away.

Unfortunately, raking the mess of autumn away deprives the plants that live in the garden of the abundant decomposing organic matter that they expect to be delivered this time of year. The soil is left exposed and uninsulated, allowing temperature and moisture content to fluctuate more than they would naturally. Nutrients are not replenished as readily as they would be from decomposition.

Mulch, which can be applied at any time of the year, is quite seasonably appropriate in autumn. This is when plants expect decomposing organic matter to arrive from above. Mulch compensates for the loss of what we consider to be a mess, but what plants consider to be an important component to their natural ecology. It gives them what they want, but is neat enough for refined gardens.

The best mulch for the job just might be fallen leaves that were raked last year and composted, perhaps with other debris from the kitchen and garden.

To Mulch Is Not Enough

60727thumbMost plants would prefer the real thing; how they do it in the wild. They drop their leaves, flowers and twigs. Deciduous plants do it mostly in autumn. Evergreens might spread it out through the year. The debris accumulates on the ground below, and decomposes at about the same rate as it accumulates. There is no one there to clean it up. Yet, the natural ecosystems know what to do.

The plants that produce the debris use the nutrients produced by its decomposition. So, with the help of the many microorganisms in the soil, they recycle their own trash. To exploit this resource most efficiently, feeder roots tend to congregate near the surface of the soil where the nutrients are. Because the debris also insulates and shades the soil surface, roots are comfortable there.

Densely forested ecosystems produce the most debris. Many smaller plants in such ecosystems may disperse their roots exclusively into decomposing debris without reaching into soil below. In desert ecosystems, where such debris is minimal, roots are mostly dispersed much deeper to avoid the hot and dry soil surface. They wait for recycled nutrients to leach to them through the soil.

Redwoods, cypresses, many pines and most eucalyptus produce unusually thick layers of debris that decompose slowly. This technique inhibits or prevents the germination of seeds of potentially competitive plants. So, in other words, these trees and other plants had this, as well as moisture retention, soil insulation and nutrient recycling, all figured out long before we knew about mulching.

After we put so much work into raking and disposing of foliar debris that would otherwise accumulate in our gardens, it is ironic that we sometimes need to apply seasoned mulch to compensate for the lack of organic material on the surface of the soil. (Unseasoned mulch draws nitrogen from the soil to sustain its own decomposition.) It does more than merely improve the appearance of otherwise exposed soil. Mulch helps unnatural landscape environments function a bit more naturally.