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.
Almost everyone on the West Coast of California has encountered silver wattle, Acacia dealbata. Some of us know how resilient it is to most methods of eradication. The more fortunate enjoy its magnificently bloom from a distance. It is almost never planted intentionally. It is an aggressively naturalized exotic species. Most grows wild near roadside ditches. Some invades home gardens.
The profuse and bright yellow bloom of silver wattle is spectacular while most deciduous trees remain bare late in winter. Big and billowy trusses of smaller round floral structures obscure most of their slightly grayish foliage. The many individual staminate flowers within this impressive bloom are actually minute. Their hearty floral fragrance is appealing to some, but objectionable to others.
Silver wattle lives fast and dies young. Some trees are so vigorous while young that they are unable to support their own weight. Without appropriate pruning, they simply fall over. Even stable and structurally sound trees deteriorate after about thirty years. Few survive for fifty. They seed prolifically though! Mature trees can get forty feet tall. The finely textured foliage is bipinnately compound.
‘A Tree Grows In Brooklyn’ documents the resiliency and invasiveness of the common but typically undesirable tree of Heaven, Ailanthus altissima. Once a single female tree get established, the extremely prolific seeds get everywhere, including cracks in concrete. The resulting seedlings conquer wherever they are not dug out. If cut down, they just resprout from the roots.
Male trees smell horrible while blooming for about a month in spring or summer. They are pollinated by flies, so naturally smell like what flies like. The tiny yellowish or tan flowers hang on panicles that can be a foot and a half long. Female blooms are not as big, prolific or objectionably fragrant. However, stems, leaves and all other parts of both genders smell rotten when handled.
Tree of Heaven, which has earned the alternative names of ‘tree of Hell’, ‘stink tree’, ‘ghetto elm’ and ‘ghetto palm’, is no longer a tree that gets planted by choice. It is typically a tree that plants itself, and on rare occasion, happens to grow into a good situation. They should not be allowed to overwhelm more desirable trees, or get too close to concrete or other damageable features.
Young trees grow very fast to about forty feet tall. Older and slower trees do not get much taller, although sheltered trees can get twice as tall, with elegant gray bark. They do not live much more than fifty years. The big pinnately compound leaves are surprisingly pretty. On vigorous shoots, individual leaves can get as long as two and a half feet, with leaflets as long as six inches.
Pretty weeds do not get my attention like they do for others. They look too much like weeds to me. If I want to appreciate them, I must do so with intention. Sometimes, I do actually try. I did happen to notice these two weeds. However, now that I got their pictures, I have no use for either of them. Neither is readily useful for the gardening column. I will just share them here.
The yellow flower pictured above is most likely prickly lettuce. I really do not know. I know it as yellow chicory; but chicory does not bloom yellow. Some people think of it as dandelion, since the flowers are similar. These flowers stand much higher though, with only minimal foliage below. For the picture, I plucked this flower and stuck it in the ground to keep it still in the breeze.
The white flower pictured below is common bindweed. When I was a kid, I knew it as morning glory. In this close up picture, it looks like a fancier garden variety of morning glory, although the flower is much smaller. Real morning glory happens to look good in white, like this one does. If it is fragrant, I have never noticed. It tends to creep along the ground more than it climbs.
It sometimes seems silly to me that others so easily notice how pretty weeds such as these are, especially while there are so many more flowers that are prettier. Then, I realize what others must think of what I consider to be pretty. For example, the pollarded blue gum with aromatic blue foliage that I enjoy so much, is the same species that gives all eucalypti a bad reputation.
Besides, these flowers were the prettiest in the otherwise bare meadow where I found them.
Dracunculus vulgaris make a sinister impression by botanical name alone. Common names include dragon lily, dragon arum, dragonwort, black dragon, snake lily, stink lily and voodoo lily. That makes it sinister enough to be compelling. Although rare in nurseries, dormant tubers are available in season by mail order. Alternatively, established colonies happily share a few dormant tubers.
Dragon lily is quite easy to grow. It appreciates rich soil and regular watering, at least until it gets established. Once settled in, it might be satisfied with only monthly watering until it goes dormant in late summer. Because it prefers humid climates, it wants shelter from wind here, and may like a bit of partial afternoon shade. It is so adaptable that it unfortunately naturalized in some regions.
The fragrance of dragon lily attracts insect pollinators that are drawn to dead animals. Those of us who enjoy unusual plants find it amusing. Everyone else thinks it stinks. Blooms that produce the fragrance are spectacular, with a big and flared purplish red spathe around a slender black spadix. They may stand nearly three feet tall, among lightly blotched and deeply lobed palmate leaves.
The small yellow flowers are the giveaway. Real strawberries have white or maybe pink flowers. Otherwise, mock strawberry, Potentilla indica, looks very much like wild strawberry, with similar small red fruits and neatly serrate trifoliate leaves (that are palmately divided into three leaflets). The berries are edible, but do not taste like much.
Like real strawberries, mock strawberry spreads efficiently by stolons. If watered occasionally and sometimes fertilized, it is probably a better groundcover than the common ornamental varieties of wild strawberry. It is invasive in some areas.
Shortly after silver wattle finishes blooming up high, any of four species of broom begin blooming down low. Brooms and silver wattle often naturalize together. All bloom with the same delightfully brilliant yellow. The four brooms are French broom – Cytisus monspessulana, Scotch broom – Cytisus scoparius, Portuguese broom – Cytisus striatus and Spanish broom – Spartium junceum.
Sadly, none are desirable species. All are exotic weeds. They are only a topic for gardening because they are so aggressively invasive. Not only do they overwhelm and displace native species, but they also enhance soil nitrogen to promote the growth of other exotic weeds! They are unpalatable to deer, and are not bothered by insects or disease. Furthermore, brooms are combustible!
It is best to enjoy their cheery bloom from a distance, where they grow wild where they really should not. The various species tend to dominate distinct regions, with some degree of mingling. Big specimens can get eight feet tall, but do not live long as they are replaced by herds of seedlings. French broom is the only evergreen species; but any can defoliate in response to hot dry weather.
Under a bank of carpet roses that I am none too keen on, this grubby ground cover competes with more aggressive weeds. To me, it looks like common mock strawberry, Potentilla indica. I never gave it much though. It seemed to me that whoever had installed cheap and common carpet roses on that bank would have employed a comparably cheap and common ground cover.
The ground cover was more prolific in open spots that were too narrow for more of the roses, and from there, seemed to have migrated under the roses as a second layer of ground cover. It would not have been installed underneath intentionally. It did not occur to me that it may have grown from seed like so many other weeds there, or migrated in from the surrounding forest.
The white flowers did catch my attention though. I was not aware of a mock strawberry that bloomed with white flowers. I really was not concerned enough about it to investigate. This part of the landscape will be getting renovated soon anyway. The roses will be relocated to where they can not extend their thorny canes into an adjacent walkway. Agapanthus will replace them.
Now that I am seeing more of these odd strawberries, I am wondering if this low ground cover that I formerly had no regard for is actually the native wild strawberry, Fragaria californica. Not only should mock strawberry bloom with yellow flowers, but it should also produce more spherical berries. Now I will need to identify it before I either dispose of it, or merely relocate it.
I prefer to not salvage exotic species that exhibit potential to naturalize from landscaped areas into surrounding forests. If this ground cover is wild strawberry, it migrated from surrounding forests into a particular casually landscaped area.
Poison ivy is not native here. Neither is English ivy. However, English ivy, Hedera helix, is an aggressively naturalized exotic species. Even after it had been designated as a voracious weed in the region, it was installed in some of the landscapes here many years ago. It is so common here now that we know it simply as the standard ‘ivy’. Algerian ivy was planted too, but it is not quite so aggressive.
1. English ivy grew up and over this abandoned building, and accelerated the deterioration of the old roof. It would be pointless to remove it now. The building will eventually be demolished.
2. This building is not abandoned. No ivy was on this roof just a few days earlier. All this ivy did not grow up and over the building this aggressively since then, but fell from above. Surprise!
3. The yellow pointer shows where the dead redwood trunk that supported all the ivy broke and dropped the whole mess onto the roof at the bottom of the picture. It is about thirty feet up!
4. What a mess! This close up of the same broken dead redwood trunk shows another dead redwood trunk to the right, and a viable trunk with another dense ivy thicket in the background.
5. Surprisingly, this is the worst of the damage. It was likely impaled by the rotten redwood trunk. The ivy likely stayed connected to the rest of the thicket long enough to slow the descent.
6. Even after getting Ginsu with saws and shears, and getting bounce-house with debris, the pulpy redwood trunk and ivy was still a full load. That was a lot of weight to land on an old roof!
This is the link for Six on Saturday, for anyone else who would like to participate:
Montbretia showed up here several years ago. Of course, it did not take long for it to get very established. It is too shady for bloom, but not shady enough to inhibit vegetative proliferation. Those nasty stolons get everywhere, and grow into corms. They are so aggressive that they exclude English ivy! Seriously, they are the only species we know that can crowd out English ivy!
Some consider Montbretia to be the the genus name. Some consider it to be a common name for the genus of Crocosmia, or for a particular intergeneric hybrid. What is now so aggressively naturalized here might be Crocosmia paniculata. I really do not know. The few rare and sporadic blooms look like what I am familiar with in other landscapes, with branched inflorescences.
Now, I am aware of how aggressive their stolons are, and that their stolons swell into corms when they get to where they are going. I also know the physiology of simple corms, and that new replacement corms develop on top of old deteriorating corms. They might extend a few more stolons in the process, or put out a litter of cormels off to the side, but their technique is limited.
Well, it should be.
The technique demonstrated by this picture is weird. It seems to show a series of corms from the last twelve years. That makes sense if one corm replaces a previous corm annually. Longer accumulations can be found in older colonies. However, montbretia infested this landscape less than a decade ago, and took a few more years to disperse where these corms were unearthed.
Furthermore, after a decade, the oldest corms should be rotten and decomposed. Except for the stunted four year old corm, those that developed in the last six years seem to be suspiciously fresh.