Westway Horticultural Society

Termite Tips for Gardeners
by Rosemary Tessier

Termites are insects that have a place in nature as all organisms do: they recycle dead wood so that it returns to the soil more quickly than it would through natural rotting.  Unfortunately, they cannot distinguish between a dead tree branch on the ground and  a piece of lumber that is an integral part of a fence, arbour, tool shed, or house.  And why should they?  They have been around for millions of years, doing what they are good at doing. We humans are an afterthought, messing up the natural environment and expecting nature to conform to our convenience.  Termites take us down a peg, especially when they start munching through our homes.

Much information is available on the many varieties of  termites: their physiology, social organization, etc. It is also easy to find material on how homeowners can recognize their presence in their homes and what alternatives are available to remove them.  But there is little on why gardeners should be aware of termites and how some gardening practices may encourage them to move into our yards and even occasionally spread them to other yards.  This article hopes to address these issues, especially for gardeners in southern Ontario.

The following cities and towns in southern Ontario have experienced termite infestations: Amherstburg, Brampton, Dresden, Elmira, Elora, Fergus, Guelph, Hamilton, Innisfil, Kitchener, Kincardine, Leamington, Markham, Mississauga, Pickering, Oakville, Oshawa, Toronto and Windsor.

Historical Perspective

In southern Ontario, the particular species of termite we need to worry about is the eastern subterranean termite (Reticulitermes flavipes, to give it its proper name).  It is not native to our part of North America, but entered southern Ontario both in the area of the Toronto harbour and in southwestern Ontario decades ago.  They were first detected in Toronto in 1938 on the east side of the Harbour near Cherry Beach, probably having arrived as hitch-hikers on wooden crates coming from the U.S. 

It is interesting to review maps of their progress through the decades.  A map of infestations in 1953 shows six separate areas, all south of the Bloor St./Danforth line, but spreading from Jarvis to Broadview (crossing the Don River). It is significant that these are not adjacent areas, but quite discrete separate spots.  By 1962, there were 28 separate infested areas, as far west as Etobicoke, the most western borough of then Metro Toronto, and as far east as Scarborough, the most eastern.  By 1988, infestations appear on maps including Oakville to the west and Pickering to the east, and in Markham and Brampton, north of the GTA.

How are these infestations spreading?  If left to their own devices, colonies will spread, but they do not hop from spot to spot.  It is true that these termites under optimum conditions will go through a winged phase during which a couple will mate and start a new colony.  However, research done in southern Ontario seems to indicate that because our area is on the edge of acceptable climate conditions for these insects, they rarely if ever establish new colonies this way. Occasionally, it could happen that a winged pair mates and starts a colony but it appears that our cold winters destroy these small colonies before they have a chance to really get started.  From this research, it seems reasonable to conclude that during the past six decades in the Toronto area, humans have been helping move these insects to new locales.  And unfortunately, gardeners have probably been among the helping hands.

Basic Facts

Gardeners need to know some basic facts about these insects. Subterranean termites live in the ground; they need to remain protected from light and in a damp environment. They tunnel though the soil, looking for dead wood that they can reach while remaining protected underground. They are small creatures, about 5 or 6 mm. (one-quarter of an inch) long.  When they start to invade a property, their presence may not be apparent for years – sometimes decades. They are quite willing to tunnel into and consume pressure-treated wood; they will also readily eat other forms of cellulose like paper, fibreboard, cardboard and even some noncellulosic materials like polystyrene, rubber cable insulation and fabrics. They need moist wood to eat and to nest in; the more they find to support their lifestyle on your property, the more they will move in and multiply.

Gardeners take note

In cities like Toronto, with large termite infestations, gardeners should avoid providing termites with what they need.  This means choosing stone or bricks rather than wood for retaining walls, flower bed edging, stairs, etc. Wooden planters like half-barrels should not sit directly on the ground but rather be supported by bricks or patio stones.  Wooden fences, arbours, tool sheds, etc., should all be constructed to avoid direct wood to soil contact. Tree stumps, which many of us camouflage cunningly with plant pots or garden ornaments, represent nirvana for termites: excellent food and nesting facilities in one spot. Stumps should always be completely removed from the property.

We know it is good gardening practice to prune out dead wood from shrubs and trees, but we also need to make sure we get rid of the dead branches.  We are sometimes advised to pile up pruned branches and small logs in the back corners of our gardens to provide shelter for wildlife like toads and snakes and even birds.  Unfortunately, we could also be providing potential food and nesting sites for termites.  

Wood mulches can also be a mixed blessing.  Gardeners have been encouraged during the last decade to use mulch and many of us use the shredded wood mulches commonly available.  Unfortunately, using these products in a flower bed right beside the foundation of a house is probably a bad idea.  The mulch is not only a potential food source; it also provides a sheltered pathway up to the foundation, where any crack or crevice leading to a bit of wood can provide a entry point.  It is better to use a stone mulch such as pebbles or gravel, not wood.  Using wood mulch in other areas of the yard would be less risky but if you live in an area where you know others have termites, you probably should consider getting rid of it entirely.           

Plant Exchange

Another common practice among gardeners is the exchange of plants; just about any    gardener is happy to share a plant with a friend.  Taking a cutting is perfectly safe, but many of us will instead in the spring or fall dig up a perennial or a small shrub and divide it, giving parts to friends.  But if termites have already set up housekeeping in that yard, the gift of a plant might also start a new termite colony.  It is important to note that “might” does not mean “absolutely will”. But it is reasonable to conclude that since subterranean termites live in the soil, and since plants moved with roots will take soil along, moving plants from a property with termites will always carry some risk of moving the insects. The most potentially damaging situation is when a gardener does not yet realize that termites are on the property, and digs up and donates plants to sales or friends, oblivious to the possible damage.  The risk in any one flower pot of soil and plant is undoubtedly low. However, given the devastating effect on the homeowner if the insects eventually gain entry to the house, any responsible gardener will want to avoid giving the problem to another homeowner and another  neighbourhood

But gardeners have always wanted to share plants with friends.  Some of us have plants from divisions made by grand-parents and handed down in families.  And, horticultural societies (also called garden clubs) have always encouraged members to exchange plants and donate them both for community projects and for the plant sales that raise needed funds to carry on.  Can we reconcile the risks of termite transfer with the desire to share plants?

Recommendations

Knowing their habits makes it easier for a gardener to assess the risk of termites on the property and of termite transfer when donating plants.  Do you have termites in the neighbourhood? Do you have any tree stumps or other large pieces of dead wood on your property?  That combination should be enough to make you cautious.  The best tactic is vigilance.  Look carefully at the soil especially when digging around unprotected wood in damp areas. When digging up old shrubs such as forsythia, lilac, wisteria, weigela, Virginia creeper, evergreen shrubs, etc., do a close inspection of the roots. Remember that roses and raspberries, which have old dead-wood canes, are particularly attractive to termites. Look for insects about one-quarter inch in length, creamy white in colour, fatter than your typical ant, and slow-moving.

Consider establishing monitoring stations, that can be checked periodically.  (If any termites show up in the yard, it is essential to have your house checked immediately by an inspector).  If you live in any southern Ontario city, whether you realize it or not, you are not far from these termites, so be aware.

If one of your neighbours has termites, monitor your soil conditions closely.  Again, look in the spots where they are most likely to find wood, especially damp wood to feed on and nest in.  You will be advised by termite experts to remove all wood that could be a food source, and elevate firewood above the soil.

If termites do appear on your property, do not dig up plants in your yard and move them elsewhere (this is certainly what the companies that fight termites with pesticide will tell you).  If your house is treated and yard wood is eliminated, and after several years of monitoring no further termite activity is detected, you could consider being a plant donor again. But in fairness to the public, you should inspect any root ball you dig up very carefully.

If you are a member of a horticultural society or garden club, you are probably in the habit of donating plants frequently to other members, for special community plantings and for plant sales, and you are used to receiving plants as well.  The degree of vigilance required depends on the frequency of termite infestations in your neighbourhood.  Here are some suggested guidelines:

1.      If you are given a plant, you should always check the root ball for small, white insects, about the size of small ants.  Use a magnifiying glass if you don’t trust your eyesight, although termites, at 5 – 6mm in length are large enough to be seen by the naked eye. (Springtails and barklice, in the 1 – 2 mm range, are sometimes confused with termites, although they are much smaller).      

2.      If you want to donate plants to a plant sale or other club activity you  should do a close visual inspection of the root balls of the plants you dig up before potting them up and giving them to anyone. 

3.      If you simply want to dig up a plant to give to a friend, obviously the same applies.

4.      If you are on the executive of a hort club that holds sales, you should make your membership aware of the situation; encourage them to establish a monitoring system, which is to their advantage anyway, as homeowners. 

5.      If your club draws its membership from an area in the GTA which has a fair number of known termite infestations, you should in fairness to the general public be even more proactive about inspecting the root balls of plants used in sales or community projects.  Some senior members with possibly deteriorating eyesight might need help with soil inspection from others in the club. 

Conclusions

If you are a gardener in a city in southern Ontario, where these non-native termites continue to spread to new locations, you can adopt sensible approaches to minimize the spread of termites into your own yard.  You should also be sensitive to the dangers of moving termites when you dig up plants to give to friends or donate to a plant sale, especially if you live near infestations.  A little bit of knowledge and common sense will go a long way to help prevent the spread of termites in our  neighbourhoods.

Acknowledgement: this article was prepared with the valuable assistance of Professor Tim Myles, Director of the Urban Entomology Program at the Centre for Urban and Communities Studies at the University of Toronto.