12 Great Garden Tips for Autumn

In the midst of a particularly difficult year, there was a surge of interest in gardening. Experienced gardeners already know the autumn routine — but new gardeners may have questions. Below are twelve tips for autumn garden tasks.

1. How to Store Produce

Every crop has optimum storage conditions that maximize post-harvest lifespan. The main conditions that we attempt to control are temperature and relative humidity (RH). Store most vegetables as close to 0°C as possible, without freezing, and at as high a humidity as possible (up to 95% RH), without condensation forming. The exceptions to this are warm season and fruiting vegetables, such as tomato, pepper, squash, and pumpkin. These crops prefer temperatures in the low teens, and drier air (about 65% RH).

2. Bulbs: Which to Dig; Which to Leave

Not all perennial plants that come from underground plant parts (e.g. bulbs, corms, or tubers) can be left in the soil for the winter. In our harsh Prairie climate temperatures are just too cold for some tender plants to survive. Hardy perennials like tulip and lily bulbs are adapted to our winter conditions and can be left in the ground, coming back each spring.

Tender perennials like dahlia tubers and gladiolus corms must be dug up each autumn and stored indoors. After the tops have started to die down, prior to a hard frost, dig the plants and spread them out to dry down in a cool, dry location. Store them overwinter where the temperature is above freezing but ideally cooler that 10°C.

Click Here for more details from the Edmonton Horticultural Society.

3. Amending the Soil: When to Add Compost

Autumn is a great time to dig in organic matter, such as well-rotted manure and compost, to build up the soil for the following season. During winter they start breaking down, making nutrients more available in the spring. When adding amendments like compost be sure to understand where it came from and if there are any potential issues. Don’t add materials that might have been exposed to herbicides with a long residual action or unfinished compost with viable weeds or diseases.

4. What You Can Plant in Autumn

Spring is often cool and wet, delaying getting into the garden as early as we might like. Many plants grow at cool temperatures and may be successfully fall-seeded. Having crops like spinach and garlic in place early in the season means there is more time for growing. For fall seeding the soil should be cool enough that the seeds won’t start to germinate, aim for 5°C or cooler. Plan to plant when daytime temperatures are staying in the low single digits, any time until the ground is frozen.

5. Fall Perennial Care (haircuts, clean up, etc.)

Many gardeners prefer to clean up the garden prior to winter. Remove anything that is dead or in poor condition, apply mulches, remove debris, and trim seed heads and excess foliage. Some gardeners save these tasks until spring, leaving seed heads to feed the birds or provide winter interest. Woody stems trap snow and provide some insulation. Some perennials have leaves that survive the winter and should not be cut back. Bergenia and Japanese Spurge are examples of evergreen perennials that provide that first glimpse of green in the spring.

6. Getting the Yard Ready for Winter

Mow lawns one final time once growth has stopped (after a hard cold snap). The final height of cut should be about 5-6.5 cm. Cutting too low may damage the plant crowns but leaving the grass long may favour early spring disease growth. Rake tree leaves to remove big, heavy piles which will kill the grass underneath. Some gardeners pile leaves in flower beds for insulation, however, under wet conditions they will compress and hold moisture and low temperatures.

7. Autumn Watering

There are many schools of thought on how much water should be applied to at the end of the season, just before the soil freezes. Some plants need to be topped up, while others need to just go to sleep without being confused by lots of water. Generally, plants should be well hydrated (particularly large trees and shrubs) but should not be soaked down constantly. Autumn tends to be wetter, just keep an eye on the weather and water as needed.

Click Here for more details on late season watering practices.

8. What to Do with Dead Plants and Debris

Dead plants and debris may be composted and added back to the soil with great success. However, if debris is full of diseased material, it may be best to dispose of it elsewhere. Alternatively, a covered compost pile will protect from spores continuing to be produced and dispersing. This is a concern for late blight of potatoes and tomatoes. Succulent legumes or cucurbits with heavy levels of powdery mildew are generally best put into the garbage rather being composted. Pruned material can be chipped, burned, or removed. Black knot galls and fire-blight infected material should be removed from the site.

9. Autumn Weed Control

By the end of summer, weeding might be something that you are done with, but autumn is a good time to take a bite out of weeds. Collect and remove as many weeds as possible. Some perennial weeds (such as Canada Thistle) can be best controlled with spot sprays in the late summer and early fall. The more weeds (and their seeds) that you can remove in fall, the fewer there are to deal with the following year.

10. Autumn Garden Preparations for Spring Success.

Autumn tillage can help to incorporate the debris left from the previous crop, smooth things out somewhat, and get a start on having a better quality seed bed the following year. Do leave a rough soil surface as this may help to trap snow, improving spring soil moisture.

11. When to Prune

Pruning is something that can be done in autumn, and certainly over winter. There are many reasons to prune and many considerations based on the species of tree or shrub you are dealing with.

Click Here for a tree pruning fact sheet for beginners. 

12. Record Keeping and Mapping

The end of the growing season is a great time for reflecting on what went well and what went poorly. If you wait too long, it is easy to forget details and then have a repeat of the issues year after year. Ideally, keep records throughout the growing season, but sum it up at the end of the season if you did not do so earlier. For any part of your yard, autumn is also a great time for making plans for the following season, particularly while you remember what was planted where, and where issues occurred.

Article adapted from the Alberta Horticultural Association October 2020 newsletter and Rob Spencer, Spencer Horticultural Solutions.

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