We had a recent question about what type of mulch to use in perennial beds. We thought that others might be interested in the response:
First of all, good for you for deciding to mulch. It is a great way to retain moisture and nutrients and to slow down weeds. It is also aesthetically pleasing. After I have freshly mulched my gardens, I always feel as though I have successfully tucked all my plants into their “beds”.
You are correct in deciding not to use dyed mulch. Many dyed mulches are made from recycled and salvaged products which could include scraps of treated or manufactured lumber products. These can contain contaminants such as formaldehyde, arsenic and lead. Of course over time these leach into the soil, have the potential to run off into surface water and into aquatic environments. Also, dyed mulch is not designed to break down and of course one of the benefits of natural mulch is that it does break down and it adds nutrients to your soil. You want bacteria, fungi, insects and worms present in your soil, working hard to take the material deep down into the soil where it can be used by the plants.
You asked what type of mulch is best. I will try to give you the pros and cons of each type.
Cedar mulch is made from clippings and shavings of the bark of cedar trees. It has an insect repelling smell and its rich reddish colour looks amazing on the garden. Cedar mulch will change your soil ph only if it is green. Cedar mulch lasts a long time, in fact years. Some of the disadvantages of cedar mulch are that it also repels pollinators and benefical insects, it is expensive, and because cedar mulch breaks down slowly it has a negligible effect in improving soil nutritionness. It also loses that rich red colour and will become grey over time.
Pine mulch comes in various particle sizes from shreds to mini nuggets to large nuggets. It is relatively inexpensive and it will build the soil while it decomposes. It also retains its colour better than cedar. When used constantly over years, pine mulch can change the soil pH and use up nitrogen, affecting the growth of small plants. This can be an advantage if you are mulching around Rhododendron or Witch Hazel which prefer acidic soils.
Hardwood mulch is a byproduct of the lumber and paper industry. It spreads easily, lasts a long time and breaks down well. It will act to make the soil more alkaline, raising the pH level in your soil which you need to take into account if you are growing acid loving plants as mentioned above. Hardwood mulch can harden over time preventing rain getting into the roots. This can be remedied by fluffing it with a shrub rake.
Compost and manure used as a mulch add large amounts of organic material to the soil quickly, improving soil structure and nutrient and water holding capacity. However they do not inhibit weed growth as well as wood chips.
Some things that should never be used as mulch are sawdust, wood shavings and un-aged wood chips. As they begin to break down, they consume large amounts of nitrogen, depriving the plants of this vital nutrient.
Personally I like to layer on either compost or manure for the nutrient value. Depending on how much manure or compost I have access to, I sometimes just side-dress the perennials and then cover with a natural hardwood mulch to suppress the weeds. I enhance the soil around my Rhodendrons with a liquid fertilizer made especially for acid loving shrubs.
authored by Carol Anderson