Composting Through the Growing Season in Manitoba
Photo: Courtesy of Green Action Centre. Composting.
When and How to Harvest Your Compost in Manitoba
By Natalia Camus-Lopez, Waste Reduction Team Lead, Green Action Centre
Composting is a common practice amongst Manitoba gardeners, but questions often come up around timing—particularly when compost is ready to use and how to manage it through our seasons. With long, cold winters and a relatively short growing season, compost behaves differently here than in milder climates. Understanding how compost progresses from spring through summer, when to harvest it, and how to prepare for winter can help gardeners get the most value from their compost systems.
This article focuses on practical, season-by-season guidance for composting in Manitoba, with particular attention to harvesting compost during the growing season and preparing compost and garden beds as winter approaches.
A Brief Refresher on Composting Basics
Composting is the process by which microorganisms break down organic materials in the presence of oxygen. These microorganisms need a balance of nitrogen-rich materials (“greens”), carbon-rich materials (“browns”), moisture, and air to function effectively. In Manitoba, outdoor composting slows significantly or stops altogether during winter as temperatures drop, then resumes once conditions warm in spring. This seasonal pause is normal and does not harm the composting process.
Spring: Assessing and Restarting Your Compost
As snow melts and daytime temperatures rise, compost piles that were frozen or inactive over winter begin to thaw and reactivate. Spring is the time to assess what stage your compost is at and to restart the process.
Begin by checking the contents of your compost bin. Finished compost will be dark brown, crumbly, and have an earthy smell. If food scraps or plant material are still recognizable, the pile is warm, or if the pile heats up when turned, the compost is still breaking down and needs more time.
If you kept adding to your compost bin through the winter and chose not to layer with leaves in order to save space, that’s great—it keeps food scraps out of the landfill year-round. However, this often means the nutrient balance in the bin is off, with too many nitrogen-rich materials and not enough carbon. In spring, it’s important to correct this imbalance by adding enough “browns” to bring the compost back into balance. It’s normal for compost piles to be wet in the spring; however, if it stays wet, you will run into odour problems.
Hopefully, you still have a supply of dried leaves stored from last fall. If not, other suitable sources of carbon-rich materials include clean sawdust or fine wood shavings, shredded office paper or newsprint (nothing glossy), and even paper towels in a pinch. A useful rule of thumb is to add roughly one pound of browns for every pound of greens.
Photo: Courtesy of Green Action Centre. Compost Bin.
If you have finished compost available in spring, it can be added to garden beds a few weeks before planting. This allows nutrients to settle into the soil and improves soil structure ahead of the growing season.
If compost is still actively breaking down, it’s best to let it continue maturing rather than applying it too early. Compost that has not fully finished decomposing can continue to “work” once added to the garden. As microorganisms break down remaining material, they use nitrogen and oxygen from the surrounding soil. This can temporarily reduce the nutrients available to plants at a time when they are beginning to grow. Finished compost—dark, crumbly, and earthy smelling—will support soil health, while unfinished compost is better left to mature further in the bin.
How to Harvest Compost
The method used to harvest compost depends on the composting system.
In a single-bin system, finished compost typically collects at the bottom. Unfinished material from the top can be removed temporarily to access the finished compost, then returned to the bin to continue breaking down.
With multi-bin systems, one bin is often actively filled while another is left to mature. Once the compost in the resting bin is finished, it can be harvested all at once.
Screening compost is optional. Finer compost is useful for gardens, containers, or seed starting, while larger pieces can simply be returned to the compost pile for further decomposition.
Summer: Active Composting and Ongoing Harvest
Summer warmth speeds up composting and is often the most productive time of year. Regular additions of kitchen scraps and garden waste, along with occasional turning, help maintain airflow and even decomposition.
Photo: Courtesy of Green Action Centre. Watering compost.
Moisture management is especially important during summer. Compost should be moist but not soggy. During dry periods, compost piles may need occasional watering, while heavy rainfall may require covering the bin to prevent excess moisture.
Fall: The Best Time to Harvest Compost in Manitoba
Fall is often the ideal time to harvest compost in Manitoba. By this point, materials added earlier in the year have usually had enough time to fully decompose, and cooler temperatures make it easier to determine whether compost is finished.
Harvesting compost in fall has several advantages. Compost applied to garden beds in fall continues to integrate into the soil over winter. Freeze-thaw cycles help improve soil structure, making spring planting easier. Applying compost in fall also reduces the risk of using immature compost during the growing season.
Finished compost can be spread over garden beds and lightly worked into the top layer of soil. It can also be used as a top dressing around trees, shrubs, and perennial beds. Compost harvested in fall but not immediately used can be stored in a covered container or pile until spring.
Transitioning Toward Winter Composting
As temperatures drop, composting slows but does not stop entirely. Outdoor compost bins may freeze, which pauses microbial activity until warmer conditions return in spring. This is normal and does not damage the composting process.
Food scraps can continue to be added to outdoor bins during winter. Materials will freeze and decompose later when temperatures rise. Covering food scraps with carbon-rich materials helps manage moisture and odours.
Some gardeners choose to store food scraps temporarily in sealed containers, garages, or freezers and add them to compost in spring. Indoor composting options, such as worm composting or Bokashi systems, are also useful during winter months.
Using Finished Compost
Finished compost can be used in several ways:
- Mixed into garden beds before planting
- Spread as a top dressing around plants
- Added to containers or potting mixes
- Used to make compost tea
Regardless of how it is used, compost should always be fully mature before being applied to actively growing plants.
Final Thoughts
In Manitoba’s climate, composting follows a seasonal rhythm. Understanding when compost is ready, how to harvest it, and how to manage it from spring through fall allows gardeners to work with natural cycles rather than against them. With attention, balance, and patience, composting becomes a reliable way to improve soil health, reduce organic waste, and support productive gardens year after year.