60323Some of the biggest and nastiest weeds are thistles. The most common is annual sowthistle, which can get taller than four feet in just a few months. It is relatively easy to handle, since the bristly foliage and stems are somewhat soft, almost like coarse lettuce. Blessed milkthistle is much nastier, with sharp foliar spines that can penetrate boots! It can get more than five feet tall and broad!

Most thistles are biennials or perennials, with spiny lobed foliage. They produce low foliar rosettes during their first year, and then bolt and bloom on tall floral stalks during their second year. Biennials usually die after bloom, but sometimes regenerate from the roots later. Perennials are more likely to regenerate and bloom annually for several years. Some thistles get rather shrubby.

The roots of many types of thistle would not be too difficult to pull from well watered soil if only the spiny foliage were not so difficult to handle. Larger plants might be easier to pry out with a shovel. If foliage is merely cut off at the the surface of the soil, it will regenerate from the large tap roots left below. However, cutting down flower stalks before bloom interferes with seed dispersion.


Horridculture – Ivy League

P90306English ivy, Hedera helix, is probably the nastiest and most aggressively invasive exotic species that I work with. It climbs high into redwood trees and overwhelms understory plants (that live below the trees). It invades many of the landscapes, and worst of all, it climbs building where it ruins paint and causes rot. It grows faster than we can keep up with it.

English ivy is actually a nice ground cover plant for refined landscapes. I grew it at my home in town. Contrary to popular belief, it does not root into and parasitize the trees that it climbs. Actually, it rarely overwhelms and shades out large trees. It prefers to keep them alive for support, from which it disperses its seed. However, it does promote decay in the trunks that it climbs, particularly where it retains moisture at ground level. Native trees are not accustomed to that.

We try to remove as much English ivy at work as possible, which includes removing it from trees and buildings. So far, with a few exceptions of small bits of ivy that broke off high in the trees that it climbed, I have been able to remove all ivy from the trees and walls that I have worked on.

Others were not so fortunate. When quick and efficient removal of ivy from the bases of as many mature trees as possible is the priority, ivy is more often severed down low, and left to die on the trunks of the infested trees. It looks shabby to say the least, and takes many years to deteriorate and fall away. In the picture above, dead ivy that was severed within the past few years is already being replaced by new ivy, which will also need to be severed.

The same technique happens with ivy on buildings. It gets cut at the foundations, but left on the walls to shrivel and turn brown. The dead ivy in the picture below was reaching upstairs eaves when it was severed, and remains there a few years later.

What annoys me so much about this technique is that it does not take much extra effort or time to tug quite most of the lower ivy from trees and walls. For most situations, all ivy can be dislodged, although tiny aerial roots remain. It is much easier to dislodge while fresh than after it is dried and crispy.P90306+

Unplanned Green Roof

p90106The last green roof that I wrote about was planned, although not in a typical manner. It is still my favorite green roof. Otherwise, I am none too keen on the fad. Very few buildings benefit from green roofs, and green roofs really do take more work than conventional landscapes in the ground.

The sort of green roof pictured here was most certainly not planned. It could have been the result of a an uncleaned gutter. All sorts of weeds can grow in the damp debris that can wash off of roofs, particularly in damp and foggy coastal climates where moisture so often drips from the edges of roofs. This gutter is just a short distance from the beach in Santa Cruz. The willows in the San Lorenzo River are next door.

Knowing what I know about this particular type of willow, I would guess that the cleanliness of the gutter, or lack thereof, was not really the problem. These aggressive willows can germinate in the slightest bit of debris, even under a single leaf that did not get rinsed or blown away fast enough. Once germinated, their finely textured roots are experts at clinging to anything that might otherwise get rinsed away. If there is not enough debris and dirt for them to grow in, they simply collect their own. Now that it has started the process, it will continue to collect debris and expand its root system until it gets removed or ruins the gutter. It seems to have already collected enough debris to share with a few grassy weeds nearby. It is mostly dormant now, and might have defoliated in the rain since this pictures was taken a few days ago. However, if it stays, it will resume aggressive growth as winter ends.

Tree of Heaven

50923‘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.


P80915K.JPGJust about everything in this picture is icky! This species of pampas grass, Cortaderia jubata, is one of the most aggressive and noxious of the invasive exotic specie that have naturalized here. It seems to be incarcerated behind the weathered cyclone fence with barbed wire on top. The big water tank is is a harshly stark background. The tired old Douglas firs and ponderosa pines to the left and right seem to be unhappy here. The small coast live oak that is at least trying to make a more cheerful appearance is only oppressed by the surroundings. Only the clear blue sky above lacks the ick factor.

What is not visible in the picture is that there is no other flora in the area. Most of the area is covered with a thick layer of gravel to prevent vegetation from getting established close to the water tank. Weeds that manage to grow get cut down regularly. Only the pampas grass survives the ravages of the weed eater. It has been allowed to stay only because it has not yet been perceived to be a problem. It will probably be removed eventually as well. It would have been much easier to remove before it got so big. Now that it is blooming, it is likely to sow seed for more of the same.

Whomever gets the grim task of removing the pampas grass must contend with the nasty ‘razor grass’ foliage. The very sharp and very finely serrated edges of each leaf cause the worst sort of paper cuts! Even if handled very carefully, the long strap leaves have a way of getting everywhere. Someone tugging the base of the foliage with gloves and long sleeves can lose an ear to just one of the many long leaves that whip around so aimlessly.

However, someone who is unfamiliar with the serious nastiness of pampas grass might see this picture very differently. The firs, pines and oaks are not so bad. The water tank is a neutral background to the subject matter. The weathered cyclone fence with barbed wire on top, . . . well, let’s just say, . . . it’s ‘abstract’. Anyway, to someone who does not know better, the fluffy floral plumes of pampas grass that toss so many seed that have the potential to grow into an indefinite supply of the same nastiness are actually quite pretty.P89015K+.JPG

Scarlet Pimpernel

P80826It is pretty but pervasive. Actually, I do not really find scarlet pimpernel to be all that appealing, but this is how someone who reads my gardening column in the Santa Ynes Valley News describes it. Embarrassingly, she requested that I discuss scarlet pimpernel while it was more of a problem back on June 7, but I only recently read the message. By now, it is already dying back for autumn, and is completely deteriorated in dry and hot exposed areas. It will be back next spring, and will bloom with tiny peachy orange flowers so that it can throw tiny but ridiculously abundant seed by summer before anyone notices. Flowers can be other colors in other regions. The sprawling stems can spread more than a foot wide, and can get up to about ten inches high if sprawling over other weeds. The tiny and soft leaves are arranged in opposing pairs. Scarlet pimpernel may not seem like much of a threat now that it is deteriorating, but new seedlings will be profuse early next spring, and can compete with seedlings of more desirable plants.
Control of scarlet pimpernel is not easy. If application of herbicide is an option, it does not stick to the foliage of scarlet pimpernel very well, even with a wetting agent. Hoeing eliminated larger plants, but does not kill the seed that the larger plants have already tossed. Scarlet pimpernel starts throwing seed so early that it must be pulled as soon as it appears in very early spring. Like I said, it is not easy. The small plants are not even easy to see. The process must be repeated at least weekly for a while, just because some seedlings will emerge after the first batch is gone.
Fortunately, scarlet pimpernel is not very vigorous. If it comes up through mulch, only a few plants will survive, and they will be easy to pull. They do not compete with other more vigorous plants well either. Many simple ground covers will simply shade it out, although it can mingle with and ruin some of the finely textured ground covers like baby tears and thyme.
I am sorry that I do not have any more information about scarlet pimpernel than is commonly known. I am speaking primarily from experience, and my experience has not been as bad as with other more aggressive weeds. Scarlet pimpernel always seems to be around, but is not so much of a problem that I am too worried about annihilating it completely.P80826+

The Good Weed

P80616KOnce in a while, a stray seed of a plant that would normally be considered to be an invasive exotic species happens to grow in a spot where it happens to fit. Those of us who regularly pull up unwanted feral seedlings, are typically skeptical. We probably pull up many such seedlings merely because we do not trust them, or because we do not want them broadcasting their seeds elsewhere in the neighborhood. In our region, Acacia dealbata, blue gum eucalyptus, black locust, pampas grass, broom, poke berry and Himalayan blackberry get no consideration; and their seedlings should be removed as promptly as they are discovered. English ivy does not get much more consideration, but every once in a while, it happens to wander into a situation where it is allowed to stay.

Catalpa is one that we are not quite sure about. It is an exotic species that happens to disperse unwanted seed at times, but is not invasive enough to warrant prompt removal of all seedlings. Many seedlings appeared in the area several years ago, and most were removed because of where they were. However, if any other seedlings have appeared since then, they have been discreet enough to remain unnoticed. It was as if there was a very specific mating season. Catalpa had not been invasive prior to that, and has not been invasive since.

Two of the feral catalpa seedlings appeared on the edge of the parking lot at the Felton Presbyterian Church. One became disfigured and distressed, and finally died before being removed. The other just happened to be in the middle of a parkstrip, and in a location where a good sized shade tree had room to grow. Because no one could find a good reason for removal, it stayed. After only a few years, it is now a good sized and very well structured shade tree that blooms nicely this time of year. It may not last long, since catalpas are short lived, but for now, it is a nice component to the landscape. This weed gets a happy ending.


Blue Dawn Flower

70614Even within its native range, blue dawn flower, Ipomoea indica, can be a problem. There are not many other plants in some coastal regions of Peru that can avoid getting overwhelmed by the aggressive wiry vines. These vines grow roots where they touch soil, so can spread indefinitely over the ground. Vines that succumb to frost over winter regenerate as if nothing ever happened.

Three inch wide flowers are rich purplish blue when they open at dawn. They then fade through the day, only to be replaced by fresh new flowers the following morning. Bloom continues from spring until autumn, and can get profuse at times. The lush rich green leaves are cordate (heart-shaped) or lobed (with only three lobes). Too much fertilizer promotes growth but inhibits bloom.

Blue dawn flower’s main weakness is a dependency on water. If it gets too dry briefly in summer, it can die back like it does with frost, and then recover once it gets water, but it will not survive for very long if it stays dry. As aggressive as it is, it should not spread very far from landscaped areas or riparian areas where summers are too warm and dry for it.

Jumping Juniper!

P80519KOh, the stigma of juniper never gets old! No matter how many cool new cultivars get introduced, and how many specie get rediscovered, they are still though of as those nastily prickly ‘tams’ that were too common in the 1950s. Even some of us who really like junipers dislike tams, not only because they share their stigma with all other members of the genus, but also because they really are nasty and prickly, and not as useful as their overuse would suggest. Are they deep ground cover or shallow shrubbery? They might work for a few years, or maybe many years, but they eventually crash into each other or other plants and pile up into a dense thicket that can not be pruned without being deprived of all dignity.

In the neighborhood where I primarily work, we have a ‘do not plant’ list. Such lists typically cite specie that are notoriously invasive, such as pampas grass, blue gum eucalyptus, Acacia dealbata and English ivy. In regions where fire is a concern, specie that are notoriously combustible, such as cedar, cypress, rosemary and manzanita, are also cited. Almost all of the specie on our list are there for good reason. I mean, we can figure out why they are undesirable in the neighborhood. Then there is juniper. No specie are cited; just the entire genus. Juniper.

Perhaps the eastern red cedar, Juniperus virginiana, is too likely to become an invasive exotic here, so the entire species was condemned. Perhaps junipers in abundance are just too combustible. The ‘do not plant’ list provides no explanation.

There are a few mature junipers in the landscapes that were installed before the list was compiled. A hedge of such junipers was recently removed because it was in the construction zone of buildings being renovated. It was no loss really. They were quite disfigured after decades of reliable service. However, at one end of the hedge, there were two much younger junipers that were added relatively recently to replace one that had been removed to facilitate access to subterranean utilities. They might have been added after the ‘do not plant list’ was compiled. No one really remembers. The list was compiled a few years ago, but distributed only recently.

Before the landscape was demolished, we took a few plants that could be dug up, and canned them back at the nursery for use elsewhere in other landscaped areas. We could not just leave the two small junipers to die. We dug and canned them too. Now they are back in the nursery, with no hope of finding a home back in the landscape from which they came. They happen to be nice specimens, and are certainly NOT tams. No one remembers what species or cultivar they are. They happened to match the original hedge remarkably well, which is rather impressive considering how modern cultivars have replaced most older cultivars.

I happen to have three canned junipers already. They are North American natives. Two are eastern red cedar, Juniperus virginiana, with two very distinct personalities. The other is the Juniperus communis ‘Compressa’, which is a compact cultivar and the closest I could get to the common juniper. Apparently, the common juniper is not so common in the natural form. I already do not know what to do with these three, although the common juniper can stay canned indefinitely.

These other two displaced junipers will probably go into a landscape pretty soon, while they are not yet root-bound. They just can not go any place close to where they came from.


70426The popular wisterias that bloom so profusely before their new foliage appears in spring are Chinese wisteria, Wisteria sinensis. Others specie are rare. The impressively longer floral trusses of Japanese wisteria are not as abundant, and bloom late amongst developing foliage. American and Kentucky wisteria are more docile small vines, but their floral trusses are both short and late.

Chinese wisteria is also the most fragrant and the most colorful of the wisterias. Lavender is still the most popular and traditional color. White, pink, sky blue and darker almost purplish lavender are also available. The floral trusses, known as racemes, get from half a foot to two feet long. Double flowered cultivars never became too popular because the fluffier blooms are not as elegant. The aggressive vines can reach the tops of tall trees. They rarely strangle limbs or young tree trunks, but have the potential to do so. They are more likely to crush fences and lattice. Wisteria really needs sturdy trellises and specialized pruning for confinement. Vines that grow from seed may take many years to bloom. The pinnately compound leaves turn pale yellow before falling in autumn.