So many plants that were difficult to obtain years ago are now much more available online. The internet does more than give everyone access to nurseries and seed suppliers that sell online. It also makes it possible to communicate with others who might want to share plants and seeds from their own gardens. The advantages are obvious, but there are innate problems with so many plants being too available.
Before humans started to relocate plants all over the world, plants were much more confined to certain regions. Once relocated to new regions, some plants naturalized and became problematic for the plants that were already there. Exotic (non-native) plants often had the advantage because pests that troubled them back home had not come with them.
For example, pampas grass had been confined to the Pampas region of South America. It was imported to California and Oregon because its fluffy flowers and graceful texture are so appealing. The problem now is that it naturalized, and continues to proliferate and crowd out native plants in coastal ecosystems, without natural pathogens to slow it down. The availability of so many more plants from so many more regions seriously increases the potential for the importation of invasive exotic plants, as well as plant diseases and even insects!
Another potential problem is that common names of plants can be very different in different regions. Now, this can be an advantage when seeds from a common yucca in Lubbock, Texas might actually be from the very uncommon plains yucca (Yucca campestris, which I recently purchases on Ebay!). The problem is that the yucca known as ‘Adam’s needle’ in Georgia may be a completely different species from what is known as such in Pennsylvania, Oklahoma or anywhere else. A plant described as a ‘mimosa’ could be a silk tree, a jacaranda tree, or any of several different acacia trees!
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.
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.
Working inside for most of the week has certain disadvantages, especially at this time of year. There is so much blooming that I do not go out to see. I did not get many pictures of camellias or flowering cherries while they bloomed, although some camellias continue to bloom sporadically. Some azaleas are also finished blooming. Rhododendrons are blooming nicely now, but I have not started getting pictures of them. Instead, I got pictures of a few weeds and their associates from just outside of where I work inside.
1. Broom! It is one of the most aggressively invasive exotic weeds of the Santa Cruz Mountains. No one knows if it is Scotch, Spanish or French. It is probably French, but we know it as Scotch.
2. Dandelion infests most lawns. It was probably imported for greens. I will not eat greens that grow in lawns where Rhody does what he goes outside to do. I should move some to the garden.
3. Periwinkle is a naturalized exotic species here, but is not so naturalized farther inland, or in urban areas where lacks space to migrate. I actually planted it where I lived while in high school.
4. Forget me not, as seen in the upper right corner of the previous picture, is naturalized in riparian situations, but is also too delightful to be perceived as a weed. How could anyone dislike it?
5. Pacific Coast iris is not actually a weed. It is not even exotic. This one is a hybrid of a few native species, and was planted intentionally. I would just prefer the ‘unimproved’ Iris douglasiana.
6. Rhody puts the ‘+’ in ‘Weeds +’, which is the title for this week. Perhaps this should have been the first of these six; but then no one would have bothered with the remaining five. Priorities.
This is the link for Six on Saturday, for anyone else who would like to participate:
Wildflowers have been quite a fad. Relative to most fads, they are not so impractical. For some situations, they are a good excuse to waste less effort and resources on unrefined parts of the garden. Of course, they all require some degree of effort and resources. Most are neither as wild nor as natural as their marketing suggests them to be. Few are native.
Wildflowers that lived here centuries ago, prior to the introduction of exotic species, were relatively unimpressive. Although some bloomed spectacularly, they did so within a brief season. Winter is too cool for pollinators that wildflowers intend to attract. Summer is too dry for bloom to last long. Most bloom was limited to the transition from winter into spring.
The same native wildflowers bloom even less now than they did centuries ago because of competition with exotic species. Most exotic species that compete with wildflowers are feral forage crops that lack colorful bloom. They grow so vigorously that they obscure the natives. Mitigation of such undesirable vegetation ruins wildflowers that mature within it.
Most of the best wildflowers here now are as exotic as feral forage crops. Those that are native might be more reliant on unnatural cultivation. California poppy, evening primrose, and native annual lupines might prolong bloom with a bit of extra water through summer, but need weeding. With the same watering, (non-native) cosmos stands up to the weeds.
Unfortunately, vegetation management is more important than wildflowers outside of the refined garden. Overgrown weeds are combustible and can be dangerous to pets. Weed whacking too often involves wildflowers before they get their chance to bloom, as well as foliage of spring bulbs after bloom. (It sometimes damages bark of trees and shrubs too.)
Some low and dense perennial wildflowers are more reliable than annual sorts because they exclude annual weeds. Saint John’s wort and periwinkle are invasive exotic plants, but work well as ground covers. Mowing or shearing them late in winter slows their competing weeds, and also enhances their foliar density before competing weeds regenerate.
Weeds are constantly a problem here. There is no season in which every sort of weed is inactive. As some annual types finish dispersing seed and die off for winter, others begin their season. Most weeds just happen to be most active as winter becomes spring. They try to stay ahead of desirable plants. Lawn weeds have been proliferating faster than turf.
Annual weeds were easiest to pull while still dispersing roots, and while the soil was still damp from winter rain. Biennial weeds that grew last year are more firmly rooted, even if their soil is damp. Perennial weeds are most persistent, with extensively dispersed roots. Of course, as lawn weeds, all three types are more challenging than in the open ground.
Separation of weeds from turf grass is significantly more work than pulling weeds alone. It is not so easy to reach down into the roots of the weeds. Nor is it so easy to pull weeds without pulling some of the turf grass with them. The process is likely to leave bald spots. Many of the persistent perennial lawn weeds are more firmly rooted than the turf grass is.
Dandelion is notorious for leaving bits of root behind when pulled. These bits regenerate into new plants that are even more difficult to pull than the originals. The various species of oxalis persist by various means. Some produce bulbs or offsets that are impossible to separate from the soil. Others develop thick networks of sinewy stolons that break apart.
Some persistent lawn weeds, such as plantain and English daisy, as well as many of the feral grasses, are so difficult to eradicate that they ultimately integrate into the lawns that they infest. It is simply easier to mow over them than to try to eliminate them. They never quite assimilate though, so interfere with the uniformity of color and texture of their lawns.
Unfortunately, some lawn weeds do worse than merely compromise the visual appeal of turf. Burclover and foxtail can be dangerous to pets. Their seed is designed to stick to fur. Burclover seed structures can tangle and accumulate in long fur, causing dense matting. Foxtail seed structures can lodge into eyes, nostrils, throats and ears, or pierce soft skin.
While it was busy naturalizing in Australia, South Africa and southern South America, the California poppy was getting forced out of parts of its own native range by more aggressive exotic plants that were also busy getting naturalized. Technically, any plant that is not native is exotic. Any exotic plant that becomes naturalized in a foreign environment is able to proliferate without any help, as if it were native. Naturalized exotic plants that get too aggressive become invasive weeds.
Weeds are plants where they are not wanted. This is a very broad definition that includes plants ranging from simple little dandelions in urban lawns to humongous bluegum eucalyptus in forests. Naturalized exotic weeds can be much more problematic than weeds that can only proliferate where they get watered in gardens and landscapes, because they can get established where they are not expected.
Water hyacinth that clogs the Sacramento and San Joaquin River Delta is not often a problem in terrestrial landscapes. However, giant reed, pampas grass, Acacia dealbata and blackberry brambles can infest home gardens just as easily as they infest wild lands. Because they do not need to be watered, they can get established and grow quite large in unused parts of the garden before anyone notices.
Many naturalized weeds somehow seem to much more aggressive and problematic than even the most prolific of native plants. Even the common native lupines are relatively docile compared to annual oat grass. Native blackberry may seem impossible to eradicate, but is actually neither as persistent nor as unpleasant to handle as the exotic Siberian blackberry!
Young weeds are easiest to pull now while the soil is still evenly damp, and young roots are only beginning to disperse. They will be more difficult to pull after roots are dispersed and soil hardens. Tree weeds and large perennial weeds that were cut down last year instead of pulled will likely need to be dug. Bermuda grass is a relatively low perennial grass that always seems to be difficult to dig. Mowing or cutting down annual grass weeds with a weed whacker will not eliminate them, but limits the development and dispersion of seed for the next generation. Burclover, sowthistle, bindweed, purslane, spurge and the various oxalis are some of the other common weeds that really get going this time of year.
With few exceptions, the most aggressively invasive weeds here are exotic. In other words, they are not native. They came from other regions where they were likely compliant participants of their respective ecosystems. At home, where they must compete with other members of their ecosystem, they may not be so aggressively invasive. Ecology is the opposite of a home field advantage.
Exotic species become invasive weeds in foreign ecosystems for a variety of reasons. For some, the climate is more favorable. Some grow and proliferate more freely without diseases, insects and animals that troubled them back home. There are also several that simply compete more aggressively for space and resources than native species are accustomed to. It is a jungle out there.
Most invasive exotic species are annuals. Many are biennials or perennials. Some are vines, shrubs or even trees. Most were imported intentionally, for a variety of reasons, and then naturalized. Forage and cover crops were some of the earliest of exotic species to become invasive. Other invasive species escaped from home gardens. Blue gum eucalyptus was imported for wood pulp.
Regardless of their origins or physiological forms, invasive species are weeds. They compete for the same resources that desirable plants use. They impede on the aesthetic appeal of gardens and landscapes. Some types of weeds become hazardously combustible. Even if not directly problematic, invasive weeds disperse seed that can be problematic nearby. Many disperse stolons.
Most weeds start early and grow fast to get ahead of their competition. They are more active at this time of year than at any other time. They are also vulnerable. While the soil remains damp from winter rain, they are relatively easy to pull intact. They have not yet dispersed seed for their subsequent generation. Later, they are likely to leave behind seed and bits of roots that can regenerate.
It is important to pull or grub out seedlings of unwanted shrubbery and trees, as annual weeds. They are likely to regenerate if merely cut.
The coloring of foliage is a bit slow this autumn. The cooling nights after such warm weather is bringing some of the deciduous foliage down while it is barely yellowing. Honeylocust and black oak have already gotten notably sparse without much notable color. Hopefully, the more colorful sweetgum, flowering pear, pistache and gingko trees will retain their foliage later into cooler weather, so that they can put on a worthy show before filling compost piles.
It is probably slightly too early to clean gutters and downspouts. Unless the rainy season somehow starts first, this should probably wait until most of the foliage that is expected to fall has already fallen. Lawns, certain ground covers, decks and pavement should be raked as needed though. Decks and pavement can get stained from the tannins that leach from decomposing foliage. Lawn and ground cover do not like the shade under the debris.
However, slugs and snails really dig the mess. Fallen foliage keeps the ground cool, damp and shaded. Raking leaves does not eliminate slugs and snails, but inhibits their proliferation. There are always plenty of other hiding places. As the weather eventually gets cooler and damp, snails that stay out in the early morning should be collected and disposed of. Of course this technique is not convenient for everyone, since most snails hide before the sun comes up. Small slugs hide earlier in the morning and are even more unpleasant to handle.
Once found, neither slugs nor snails are too elusive . . . or fast. Yet, plucking and collecting them is not a fun job. Once collected, no one knows what to do with them. They can be put into plastic bags and disposed of; and will eventually succumb. Some people prefer to simply toss them onto a dry and sunny driveway or roof where they succumb more quickly and get taken by birds. Snails may need to be squashed to limit mobility.
Even though it is too late to prevent most types of weeds from dispersing their seed, a few types continue to disperse seed as they deteriorate through autumn and winter. Weeds in areas that get watered last longer and disperse their seed later than those without watering. Perennial weeds that are still green in dry areas areas will be easier to pull after the first rain.