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.

4 thoughts on “Thorny Vegetation Is Naturally Repellent

  1. At first, I thought your top photo was white wisteria. It’s quite beautiful. Another non-native plant that’s used for defense from time to time is Trifoliate Orange. It grows down here, but the University of Oklahoma (I can’t remember which campus) used it for security fencing around their buildings.

    Liked by 1 person

    1. Oh, that is wicked! When I grew citrus trees, trifoliate orange was used as understock for some of the more unusual cultivars that we did not grow many of. Shaddock, which was the primary understock that was used for all the common cultivars, has much bigger thorns.

      Liked by 1 person

  2. My father told of a Native American legend. Roses didn’t have thorns. The great spirit loved roses but the rabbits ate the plants. He loved rabbits too, but wanted to have roses. So he put the thorns on the roses, and then he had roses, and rabbits. Just an old legend, but it’s nice.

    Liked by 1 person

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