Armed with needle-tipped leaves with saw blade edges, agave forms an impenetrable barrier to all but the most suicidal burglars. Place these under a window and nobody is climbing in!  Photo: Daryl Mitchell

When you go to bed at night, do you triple-bolt your doors, lock your shutters, jam chair backs under your door knobs, and play recordings of howling hyenas? Home security is a major worry these days, but did you know that certain plants can protect your home? If you're looking for creative home security alarms, here are some borderline lethal suggestions to make even the most desperate criminal consider becoming a nun.

Scary Plant #1 -- Agaves (above) Mostly native to Mexico and the desert Southwest, these succulent perennials with spear-shaped leaves are nature's answer to the blood bank. One species, blue agave (Agave azul), is the source of a wonderful elixir named tequila. Another called century plant (Agave americana) gets its name from supposedly blooming only once every 100 years. What you need to know is if you fall on the spines of either, you will be screaming for tequila as you hang there for what seems like a century.

Agaves are easy to grow, needing only sun and well-drained soil (especially in winter). Cold-hardiness is a limiting factor, as many species won't take temps much below freezing, but Tony Avent of Plant Delights Nursery in North Carolina has assembled a rogue's gallery of cold-hardy agaves (to Zone 7) perfect for planting under vulnerable windows and porches. Try the voracious Agave gentryi 'Jaws', the horrific Agave horrida, the vicious Agave 'Mako Shark', or the electrifying Agave striata 'Live Wires.'

Scary Plant #2 -- Hardy Orange

emHardy orange doesn't easily surrender its fruits. Do you feel lucky? Photo: Kristine Paulus/em

Hardy orange (Poncirus trifoliata) is the world's most cold-hardy citrus, withstanding temps as low as -20 degrees. In spring, it produces fragrant white flowers followed by very aromatic (though inedible), orange-yellow fruits. But what really makes every encounter with this large shrub a memorable one are the long, stout, needle-sharp spines that arm every inch of its bright green branches. Many years ago, Grumpy accidentally fell on top of one while pruning. His DNA is still all over it. Call me a universal donor.

Growing up to 20 feet tall and 12 feet wide, hardy orange loves pruning and, therefore, makes a super-malevolent barrier hedge. Trust me, no one is sneaking through or over this baby. You can also espalier it against a wall to create a spiny fortress.

Scary Plant #3 -- Silk Floss Tree

emLove hurts. Photo: Allen Rokach/em

Ever wonder what savage tree trunk an obviously drug-crazed Grumpy is hugging in this old photo? Depending on your preference, it's either called a silk-floss tree or floss-silk tree (Chorizia speciosa). It gets its name from the soft, fluff-covered seeds that follow the spectacular pink to red blossoms that appear on leafless branches in autumn. But I think it should be called vengeance tree.

Some trees are fun to climb. This is not one. Thousands of brutal, stout spines arm its trunk, each demanding its own pound of flesh. So if you plant this 50-footer near your house, don't worry about burglars climbing up to the roof or second-floor windows. Heck, don't even worry about squirrels. Silk-floss tree is semi-tropical, so you can't grow it outside or south Florida or south Texas. Which is kinda too bad. Pain like this should be shared.

More Scary Plants to Punish Ne'er-do-wells If you can't find any of the above plant ninjas at your garden center, here are 10 more evil spiny, thorny offerings to deter home invasion. Consider them armed and dangerous. BWAHAHAAHA!!


Chinese Holly (Ilex cornuta)

Firethorn (Pyracantha sp.)

Hawthorn (Crataegus sp.)

Honeylocust (Gleditzia triacanthos)

'Knockout' rose

Needle palm (Rhapidophyllum hystrix)

Prickly-pear cactus (Opuntia sp.)

Spanish bayonet (Yucca aloifolia)

Wintergreen barberry (Berberis julianae)