I keep reading that in the fall it’s best to chop up leaves and spread them as a mulch over your garden bead. However I have a horrible aphid problem so I have always raked up and bagged the leaves. So if one has a pest problem, is it still best to rake them up or should I ‘leave’ them?
Thank you for contacting Toronto Master Gardeners.
You have asked two questions here one about an aphid problem and about one about raking leaves in the fall.
Aphids are a big problem for many gardeners. There are several ways to fight back against the aphid. One is with chemicals. If this is the root you choose you will need to consult your local nursery to find out what is available in your location. Another technique is to hit them with a blast from your garden hose to remove them and their honeydew. You will probably need repeated blasts for maintenance. Another technique is to use other insects that prey on aphids. You will see places selling lady bugs for release in your garden. This technique is hotly debated as you will be releasing a ladybug that is not from your region that will most likely fly away. There is no guarantee they will feast on your aphids. Many argue it is best to encourage local populations to feed on your aphids. Aphids like a high nitrogen environment which can be created through fertilizing. You did not mention if you use fertilizers, if so you may want to look at the product you are putting in your gardens or on your lawn. Lawn fertilizers are high in nitrogen.
There are many different types of aphids each with its own plant preferences. Aphids over winter on their primary host plant not in leaf litter. For some this means apple trees or roses for some and for others common weeds. If you can identify your aphids you may be able to figure out if you have one of the primary hosts on your property. A local nursery should be able to help you ID your aphids or have suggestions of where you can go in your area to find answers. There are many natural predators in your yard that feed on aphids. Three examples are stingless wasps, syrphid flies and ladybugs. Syrphid flies and ladybugs do over winter in leaf litter.
Whether to rake up your leaves is another question. There are several factors to take into account. If you have experienced any infections in your plants this summer then you should remove all infected plant debris to minimize the risk of the infection recurring next year.
Different leaves can have a different effects on your lawn and gardens. The large Norway Maple leaves are dense and can smother a lawn and may emit a chemical that deters other plants growth. Black walnut has a chemical that inhibits growth of other trees and perennials so should also be removed. There are many of the local trees that have small leaves and still allow air to get to lawns. Ultimately the volume of leaves is important. If there are too many and you are worried about your lawn you can rake them into the gardens to serve as a protective winter mulch and home for overwintering insects. Many people with large volumes of leaves will mow their leaves so the pieces are small and break down easily into the lawn. Some people will also rake there leaves into compost piles and store them for future use.
Leaves are a wonderful source of nutrients for the lawn and garden and can easily be recycled back into your gardens and lawn. Whether you leave them to break down or mow them into mulch does depend on which trees you have , the volume of leaves and the spaces you have on your property.