I am going to use this as an opportunity to help her and others with this biting problem.
I will start with the Corymbia citriodora, or Lemon Eucalyptus, also known as Lemon Scented Gum, and Blue Spotted Gum. There are some sites that still refer to it as Eucalyptus citriodora.
Corymbia citriodora
The U.S. Centers for Disease Prevention and Control has now approved oil of Lemon Eucalyptus, also known as p-menthane 3,8-diol or PMD, as an effective mosquito repellent.
This evergreen tree is native to Queensland, Australia. In nature the trees will reach anywhere from 75-100 ft. Even though it gets very big in nature, it's size is easily controlled with selective pruning. It will even flourish in a large container this way. The trees are hardy in USDA zones 9-11, so a greenhouse will be needed for colder climates.
Citriodora needs full sun with a well-drained soil. These trees grow in very nutrient poor soils and fertilizer is not needed. They are propagated by seed in the Spring.
The oil of the lemon eucalyptus is a natural, plant-based repellent oil that is prepared from the leaves. It is commercially compared to Citronella.
You would think that Citronella would be made from the Citronella Tree (Citronella mucronata) which is native to Chile.
Citronella mucronata
It is an evergreen tree, which can grow up to about 30 feet tall with a diameter of about 3 feet. The bark is dark gray and rough.
In its native habitat, It grows in areas of high humidity and constant rain. It is mostly found on steep slopes, and usually in shaded places where there is protection from direct sunlight. The Citronella Tree can tolerate low temperatures down to about 18 degrees and can even survive an occasional snow.
Well, this is not the source of "true" Citronella oil either.
There is another plant that has a deceptive name of Citronella Plant. It is a geranium plant marketed as "Pelargonium citrosum".
Pelargonium citrosum
The marketing suggests that if you plant this around your yard, it will chase away mosquitoes. Not only is the plant ineffective in repelling mosquitoes, the mosquitoes were seen landing and resting on the plant on a regular basis. It does have a very nice lemony scent.
Okay, I have held you in suspense long enough.....if you want to grow the "true" Citronella oil plant, look for Cymbopogon nardus.
Cymbopogon nardus
It is a coarse, clump-forming tropical grass that can grow 5-6 ft tall. Citronella grass is native to southeast Asia and grown commercially in Sri Lanka, India, Burma, Indonesia and Java. It is widely naturalized in tropical Asia and grown as an ornamental in South Florida and southern California.
It does best in full sun. It is a perennial (comes back every year) in USDA zones 10-12. It needs a long, warm growing season, and may not survive cool, damp Winters. Being that it does not spread by runners, as some grasses do, but is a clumping grass, growing it in a container is an option. Propagation is by dividing the clumps. It is not picky about its soil, it will grow pretty much in anything you give it.
As I mentioned, Citronella grass is the source of the commercial Citronella oil. The oil from this grass can be mixed with other vegetable oils and used in massages or rubbed on the skin for an insect repellent. If you are one of those that like to burn Citronella candles or incense, I have bad news for you. Studies have shown that to keep mosquitoes away, you would have to burn so many candles that the smoke would be almost intolerable.
It is also been reported that Citronella oil repels cats.
I hope this helps clear up some of the confusion about the different Citronella plants out there. Some will disagree with what I have said, they will swear up and down that the geranium works or that they burn a Citronella candle and they never see a mosquito. This may be true. It is also possible that there wasn't any mosquitoes around or that they found somebody better tasting!
Happy Growing!
Darren
