Those helpful insects | Ottawa Start

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7 • POSTED ON June 23, 2005
Those helpful insects
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In this week's gardening column, we look at the benefits of bumblebees, round worms, and other insects in your garden. Plus, Rene answers questions from our readers.

Our gardening column is published every Tuesday on OttawaStart. Read previous columns here.

Last week, before I was rudely interrupted by the chipmunk in our basement (we have not been able to catch it yet – we have not actually seen it either, but every now and again we hear little chipmunk noises coming from behind the wall so we know it is “lurking in the dark”) we were on the topic of beneficial insects.

The gardeners’ friends I mentioned last week – earthworm, dragonfly, ladybug, praying mantis, ground beetle and spider – are among the most common insects in our garden and although the list is by no means complete (I have not mentioned lacewings and certain kinds of wasps), I feel I should at least add honey bees, bumblebees and nematodes to the list.

Both honey bees and bumblebees are extremely important for the pollination of flowers. Simply put, pollination is the process during which pollen moves from the male parts of a flower to the female parts of another flower, thus enabling it to set seed and/or fruit.

Most plants are unable to take care of this process themselves – as flowers cannot move – and therefore rely heavily on pollinators such as insects, butterflies, birds, bats and wind (technically, human manual pollination should be included in this list). In fact, the only plants that don’t need help from insects to pollinate are ferns, mosses and fungi (as in: mushrooms). They produce spores (microscopic specks of living material) instead of flowers.

Nematodes – or round worms - are important to gardeners in an entirely different way; they can help us battle the grubs that have been damaging (and in many cases, ruining) so many lawns in our city. Nematodes are minute worm-like creatures (usually about 1 mm in length) that live in the soil. Not all species are beneficial; there are plant parasitic nematodes that actually feed on plant roots and can do serious damage to crops. As far as I know, there are no figures for Canadian crops but in the U.S. an estimated 10% of the annual potato crop is lost to nematodes.

Beneficial nematodes are now widely accepted (and available) as an environmentally friendly way to help battle white grubs and other root pests. What they do is attack the larva of the grub by entering its body and using it as a means of reproduction. It lays its eggs inside the larva and releases bacteria that initiate decomposition, thus providing a food source to the developing baby nematodes and killing the larva of the grub. Nematodes are most effective when the larvae of the grub are in their early stage (i.e. at their smallest) and therefore the best time of an application is late August or early September. Nematodes need moist soil to be successful, so it is advisable to water your lawn thoroughly before applying them (after dusk) and don’t allow the soil to dry out.

Alright, enough is enough. I am sure this last horror store will have put at least some people off their dinner so let’s move on to something a little more “appetizing”. Over the past couple of months I have received a fair number of questions. As I believe the issue involved may be on more people’s minds, I would like to share some of them with you.

Pine trees and your lawn
Recently, I received a question from Rosemary with regard to pine trees in the lawn. She has three of them and – as is almost always the case – nothing wants to grow underneath. Also, because the trees shed lots of needles and cones, that particular area always looks messy.

The problem with trees (or cedar hedges) is always that they take up so much moisture and nutrients from the soil that everything else withers and dies. If you dig around a tree or hedge you will find the soil to be very dry and sandy. No wonder; on average, a mature (pine) tree requires about 200 litres of water per day. A lawn is a constant grower and it needs water, light and nutrients to do so. However, the presence of the trees - with roots that go much deeper down into the soil - will prevent it from getting enough moisture and nutrients. To top it all off, the – evergreen – branches of the trees will also deprive the lawn of its light.

If the trees in your lawn are deciduous, planting early-flowering spring bulbs around the stems can brighten up your garden. By the time the tree comes into leaf (and starts sucking up water), the bulbs will already have produced their flowers and they will remain unharmed. Later in the season, shade-tolerant plants (such as Hosta, Fern and Lamium) will take over from the bulbs.

Evergreens pose much more difficult problems and quite frankly, I tend to choose the path of least resistance and not plant anything at all. The solution I normally recommend is to cover the area around the base of the trees with landscape fabric (available at garden centres, including those at your local supermarket or building supply stores – it is also known as “weed barrier” or “landscape cloth”) and put a few bags of shredded cedar or pine mulch (or bark nuggets) overtop. The pine needles and cones that come from the tree blend in with the mulch and everything looks tidy. Some people prefer to use gravel or rock instead of mulch, but I find that over time the needles and cones accumulate on top of the gravel and make it look messy.

Moving your plants
Another interesting question I received a while ago had everything to do with temporarily moving plants in order to make room for construction around the house. Obviously, the best time to do this is early spring when the plants have just started to grow and temperatures are still moderate. However, if you are forced to have to move plants around this time of year – or even later – there are a few tricks to give your plants a better chance of surviving.

Lesson 1: a plant “drinks” through its roots and evaporates water through itsleaves. Lesson 2: when you transplant a plant you damage its roots (no matter how careful you are). Conclusion: when you transplant a plant during a spell of hot and dry weather it cannot take in all the water it needs (because you just involuntarily mutilated its root system) but the blazing sun forces it to keep evaporating water at the same rate it did before the plant was dug up. The plant will start to wilt and without help it will eventually die.

The trick here is to restore the balance between roots and leaves by cutting the plant back hard. In chronological order: water the plant thoroughly before digging it up / dig the new hole (preferably in a shaded or semi-shaded area of the garden) and water it so that the plant will have a nice moist new spot / cut back at least 60 to 70% of the plant’s leaves and all of its flowers / dig it up and move it / water it thoroughly and keep doing this on a daily basis as long as it does not rain. This method is a bit of a “last resort” and your plants will not thank you for it but in 90 to 95% of all cases is does work.

A word of warning though: don’t attempt this twice in one season. Once the construction around your house is done, you can certainly prepare its old spot for the plant’s return by adding mulch or compost to the soil but wait with the actual moving of the plant until next spring. Plants are much tougher than you think but they’re not superheroes!

Until next week, happy gardening!

René Trim

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About René
René Trim was educated and trained in The Netherlands, before moving to Canada in 2000. After studying the differences in climate and season faced by Ontario gardeners he established Trim Garden Design and Rescue in May 2002. A gardener since the 1980’s, he has a wealth of knowledge and experience, a vast library of reference materials from which to draw answers to various garden situations as well as an enthusiastic and professional staff.