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‘Eureka’ Lemon

‘Eureka’ and ‘Lisbon’ lemons are indistinguishable.

‘Lisbon’ lemon was the original. It is still a common cultivar for orchard production of fruit for lemon products. Because almost all of its fruit ripens in winter, it can not provide fresh fruit continuously. ‘Eureka’ lemon, which is a mutant of ‘Lisbon’ lemon, may compensate. It is not as productive in season, but only because it also provides lemons out of season.

This complicates orchard harvest, but is justifiable by prolonging the supply of fresh fruit. It is more ideal for home gardens where only a few lemons are needed at a time anyway. Besides, seasonal abundance within home gardens can become too much of a surplus. ‘Eureka’ lemons are not as richly flavorful as ‘Meyer’ lemons, but are more acidically tart.

‘Eureka’ lemon trees, even on dwarfing understock, can eventually grow fifteen feet high. They are generally not quite as wide as they are tall. Their nastily sharp thorns are stout. Vigorous stems develop much longer and potentially dangerous thorns. Foliar fragrance is mild, but can be delightful during warm weather. Glossy evergreen foliage is aromatic when disturbed by lemon collection.

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Palm Reading

This is painful to look at.

Not everyone is interested in horticulture. Most enjoy other interests, such as sports, arts or cooking. They may know no more about horticulture than a garden enthusiast knows about the Seattle SeaMonkeys. Unfortunately though, some are not as aware of their lack of horticultural expertise as garden enthusiasts are aware of their lack of proficiency with other interests.

For example, I can grow just about any fruit or vegetable or perhaps grain that can grow here, but if I can not eat some of them fresh, I am aware that I do not know how to cook them. I must rely on someone who does know how. Yet, someone who is proficient with cooking is likely to believe that it is practical to grow fresh vegetables on a kitchen windowsill because it seems so easy on television gardening shows.

Someone I work with found this young Mexican fan palm to be bothersomely obtrusive to a confined situation within which he was working. He is, incidentally, a sports enthusiast. Naturally, as a sports enthusiast, he believed that he was qualified to groom the obtrusive fronds from the trunk of the Mexican fan palm. This was the result.

The necrotic but nonetheless harmless and relatively pliable foliage was removed to expose the wickedly sharp teeth of its rigid petioles, which extended outwardly in all directions from the trunk. This could have been quite dangerous for anyone who might have been so unfortunate as to bump into it. The thorns curve inward, to maximize damage to victims who pull back, which is, of course, the natural response to an encounter with such thorns. It was painful to merely look at! It seriously reminded me that I am no expert on sports or cooking. I pruned the petioles cleanly back to the main trunk.

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Barberry

Modern barberries display bold foliar color.

Its abundance of small but very sharp spines are both a blessing and a curse. Barberry, Berberis thunbergii, can work like vegetative barbed wire. An intruder might get through its thicket growth of limber stems once. Its unavoidable thorny nastiness will dissuade a second attempt. Unfortunately though, the same thorny nastiness is unpleasant to prune.

Ironically, most barberry is aesthetic rather than utilitarian. Popular modern cultivars are bright yellow or dark purplish red. Variegation is still rare. Most cultivars are less than six feet tall. Some are very dense and less than two feet tall. Old fashioned green barberry that gets ten feet tall is now uncommon. Autumn foliar color is exquisitely red or orange.

Barberry works splendidly as a low shorn hedge, although it defoliates through winter. Its naturally billowy, flaring or upright form is even more splendid unshorn. Congested older specimens regenerate vigorously after winter coppicing. Small ovate leaves constitute a refined foliar texture. Tiny bright red berries are rarely observable before birds find them.

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Thorny Vegetation Is Naturally Repellent

Black locust is painful to handle.

Roses might be more fun to grow and prune without their thorns. Blackberries are easier to pick from thornless canes. Thorny vegetation is simply unpleasant to work with. Some very desirable plants, such as roses and most blackberries, are innately thorny. The only alternative to contending with their thorny condition is to grow something totally different.

Thorns and similar structures are as diverse as foliage, with a few distinct classifications. True thorns are simply modified stems, like those of hawthorn. Spines are modified foliar structures or leaves, such as those of cacti. Prickles, such as those of rose, are modified epidermal structures. Spinose foliar margins, like those of holly, serve the same purpose. 

The purpose that thorny vegetation serves is defense. It intends to inhibit consumption of foliage, fruit or bloom. That is why some trees are thorny only while young and low to the ground, then almost thornless as they grow beyond the reach of grazing animals. Thorny trunks of honeylocust may protect seed pods from bears, so birds can disperse the seed. 

It is therefore no mystery that many of the thorniest plants are endemic to desert regions. The scarcity of edible vegetation in such regions increases the need for protection. Also, it is no mystery that most grazing animals are not too deterred by thorny vegetation to get enough to eat. Otherwise, roses and firethorn would be exempt from the ravages of deer.

Despite its intentions of deterrence, thorny vegetation inhabits home gardens for various reasons. Some produces desirable bloom or fruit, like roses and blackberries. Cacti and agaves develop remarkably striking forms. Such plants should be situated appropriately. Rose canes can be bothersome close to walkway. Agaves can be downright dangerous. 

Thorny shrubbery, such as firethorn, barberry, Natal plum and English holly, is a practical deterrent for unwanted traffic. Firethorn espaliered on the top of a fence is as effective as barbed wire, and is more appealing. Maintenance of thorny plants is more of a challenge than for thornless plants. Otherwise, thorny plants should be more popular than they are.

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Toxic Plants Are Diversely Enigmatic

Smoketree is related to poison oak.

There is no single reason for toxic plants to be as potentially dangerous as some of them are. They are toxic by various means, and to various degrees. Some actually seem to be incidentally toxic. Many are intentionally and justifiably toxic. A few live in home gardens and landscapes. Of these, a few surprisingly produce safely edible fruits and vegetables! 

Immobility is a major disadvantage for plants. Those that begin to grow where resources are inadequate are unable to relocate to more accommodating situations. Those that live within ecosystems that periodically burn must either regenerate efficiently after fire, or be resilient to fire. Flowers of all plants must rely on other organisms or wind for pollination.

Since plants are immobile, they can not evade other organisms that eat them. Therefore, some do what they can to be unappetizing for the organisms that are most threatening to them. Some use thorns or similar protective devices. Unpalatable tomentum (fuzz) works for others. Many use unappealing flavor. Some are unappetizing because they are toxic.

Toxic plants are generally not toxic to a broad range or organisms. Insects eat plants that are very toxic to mammals. Onions, although commonly consumed by humans, are toxic to canines. Fortunately, most organisms instinctively know what plants are toxic to them, and avoid eating them. Unfortunately, humans and canines are occasionally exceptions.

Because young children put random items into their mouths, and puppies chew anything that they can get their teeth around, they should not have access to toxic plants. Morning glory, foxglove, yew, oleander and castor bean are some of the more poisonous of plants that are common in home gardens. Dieffenbachia is a potentially dangerous houseplant. 

African sumac and smoketree are related to poison oak. Although not so poisonous, they are incidentally toxic allergens to those who are sensitive to them. (Incidental toxins may not be intentionally deterrent to consumptive organisms.) Hellebores are both poisonous and very allergenic. Poinsettias and their relatives are toxic because of their caustic sap. 

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Firethorn

Overwintering birds can not miss firethorn.

The most abundant bright red berries of autumn are those of firethorn, Pyracantha coccinea. They resemble English hawthorn, cotoneaster and toyon berries, but are shinier and more abundant. Their weight causes their limbs to sag. Most are either rich deep red, or brighter slightly orangy red. Orange berries are uncommon locally. Cultivars with yellow berries are less vigorous and rare.

Berry production may seem to be more variable than it actually is. Healthy plants typically produce a profusion of berries. They only seem to be more profuse if they ripen late, after migratory birds fly south. Such birds are voracious with early berries. Overwintering birds are less numerous, and consume berries slower. Regardless, few berries last long enough to deteriorate and get messy.

Firethorn is thorny enough to function as an impenetrable hedge. However, it is unpleasant to prune with all those thorns. Also, pruning without removing the stems that bloom and produce berries takes effort. Upright cultivars can get higher than downstairs eaves. Some cultivars get only a few feet tall as they sprawl over the ground. Even without berries, the evergreen foliage is appealing.

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Natal Plum

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Lush foliage hides oddly branched thorns.

The very glossy and richly deep green foliage seem to be so soft and luxuriant. Simple bright white flowers enhance the appeal. However, closer examination of Natal plum, Carissa macrocarpa, reveals impressively nasty thorn structures that are doubly branched into pairs of paired rigid and sharp thorns. That is four thorns each!

To make matters worse, all parts of Natal plum that are not fruit are toxic. But hey, they all work together to be visually appealing, even if really unfriendly. The one or two inch long evergreen leaves are quite round and stiff. The star shaped flowers that bloom as long as the weather is warm are somewhat fragrant in the evening.

Some varieties of Natal plum can reach the eaves, but most stay lower. They do not need much water, and can tolerate a bit of shade. The rosy red fruit would be delightfully colorful if it were not so rare. Manual pollination, preferably with a different pollinator, produces more of the two inch long berries that are something like mildly flavored cranberries.

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Roses Have Thorns And Thorns Have Roses

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Roses certainly look innocent enough.

Thorns, spines and prickles are not often considered to be assets. The weirdly stout prickles on the distended trunks of floss silk tree are more of an oddity than an ornamental attribute. The striking spinose foliage of agaves and yuccas can be more trouble than it is worth. After all, thorns, spines and prickles are intended to repel grazing animals.

They all work the same way, but are physiologically quite different. Thorns are modified stems, like those of bougainvillea. Spines are modified leaves, like those of cacti. Prickles are modified epidermis, like those of roses. Then there are all sorts of plants with spinose leaf margins, like English holly. Such defenses can be a nuisance to those of us who must work with them.

However, they can be useful deterrents. Natal plum that seem to be so innocent can be grown as low hedges that no one would go through more than once. Firethorn (Pyracantha) makes a larger and comparably impenetrable hedge. Their potentially dangerous thorns are almost always adequately effective with their first few pokes, before they cause too much injury.

Some plants are so dangerously thorny that they should be kept at a safe distance. Cacti, agaves and some yuccas can be strategically placed near the perimeters of large landscapes to deter trespassers. They are scary enough to be visually deterrent remotely. Mediterranean fan palm looks friendlier, but is just as mean up close.

Japanese barberry, roses and the spinose foliage of English holly are relatively safe deterrents to inhibit traffic in smaller spaces. They will keep people away from windows without necessarily blocking either access for washing the windows, or views from within. In case of fire, they are not too dangerous to escape through; although roses should not be allowed to get overgrown.

Because thorns, spines, prickles and spinose foliage are unpleasant to handle, the plants outfitted with them often get less maintenance than then should. When they get overgrown from a lack of pruning, they are even more difficult to handle. It is probably better to put nasty debris into greenwaste instead of compost. Thorns and spines are hard, so linger as foliage decays.

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Dyckia

91023It is easy to mistake various cultivars of Dyckia for diminutive relatives of Agave or Yucca. They form stout rosettes of rigid leaves with wickedly sharp terminal spines. Their comparably nasty but incurved marginal teeth resemble those of most species of Agave, but are generally more abundant. Surprisingly though, Dyckia are instead related to bromeliads. They just happen to be xeric.

Dyckia do not bloom much, but when they do, the tall and arching floral stalks really are more typical of bromeliads. As they bloom late in spring or in summer, the many small individual flowers on each stalk are collectively colorful enough to be delightfully popular with hummingbirds, butterflies and bees. Bloom is most commonly rich reddish orange, but some cultivars bloom red or yellow.

No one seems to mind that Dyckia does not often bloom. The foliage is remarkably striking alone. Many cultivars form dense mounding colonies of pups that, although unpleasant to handle, can be divided for propagation. A few toothless cultivars, armed only with terminal spines, are easier to handle. Individual rosettes can be as tall and broad as a foot. Dyckia do not need much water.

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Barberry

60817It may not look too nasty, but barberry, Berberis thunbergii, is the sort of small hedge that one goes through only once. It does not have big strong branches to hold anyone back. In fact, the limber branches are quite twiggy. The tiny spines are not impressive either, and might go unnoticed by cursory observation. Yet, they are sharp enough and plentiful enough to make quite an impression!

Because it is so unpleasant to prune, barberry should probably be planted where it has room to grow as big as it wants to without bothering anyone. If it is too close to walkways, it will either offend whomever bumps into it, or whomever needs to prune it to keep it out of the way. Mature plants will unfortunately need to be pruned eventually, so that old deteriorating stems can be groomed out.

The most popular cultivars of barberry have dark reddish or purplish foliage. A few are variegated with white; and a few have golden foliage. Green barberries are now uncommon. The tiny leaves turn bright orange in autumn before winter defoliation. Densely dwarf cultivars may not get much taller than two feet. Taller cultivars might get taller than six feet. Some barberries are very vertical.