Hi – I am redoing 3 garden beds, incorporating hydrangeas for the first time, and then sticking with the basics i.e. speedwell, lavender, phlox, echinacea, etc. I have been gardening for many years, but have never mulched. As I will be transplanting golden globe cedars and blue star junipers, I am wondering if I should mulch the transplants. Also, do you recommend mulching hydrangeas, as they are also a shrub. Now that I am renovating all of my garden beds, do you suggest mulching around all new perennials? Please advise as to which plants/shrubs will benefit from mulch and which plants may not require mulching. Would I have to replace the mulch the following spring? From what I understand, mulching has its drawbacks and is supposed to be removed in the spring on established plants…..what to do? please advise.
Dear Gardener
Thank you for reaching out to the Toronto Master Gardeners with interesting questions about mulching your three gardens. The majority of plants, especially transplants and new perennials, benefit from mulch. As seen in forests and meadows, native plants, while perhaps requiring less mulch, still derive benefits from organic mulch. Many natives have more drought tolerance due to deep roots and other characteristics.
Mulch performs a number of roles in the garden: suppression of weeds and germination of weed seeds, reduction of the need for hand weeding or chemical weed control, slowed moisture loss, regulation of soil temperature in all seasons, addition of organic matter and nutrients to the soils as mulch breaks down over time, and reduction of plant disease arising from soil containing mould and disease spores splashing back on plants from overhead watering or rain.
While there are a variety of mulches to choose from, organic mulches (e.g. wood chips, leaves, pine needles) and living (ground covers such as thyme or wild ginger) are preferred. As noted in the ‘variety of mulches’ article, use of inorganic mulch is associated with a number of issues, e.g. no nutritional benefit to soil and possible leaching of toxins.
The wording of some of the articles about removing mulch in the spring can be a bit confusing for a number of reasons having to do with when it is applied, where it is applied, the depth at which it is applied and what is meant by replacing mulch. To start with, organic mulch does not need to be replaced – it decomposes and is incorporated into the soil at rates depending on the mulch used, i.e. bark chunks takes longer to decompose while leaves, shredded with a mower, decompose faster. The article, Mulches, gives detailed information on where to use various organic mulches and their relative rates of decomposition. The depth of mulch should be no more than 5 to 7.5 cm (2-3 inches). It is important to ensure that mulch is placed no closer to the stems of young plants or shrubs than 7.5 cm to 12 cm (3-5 inches) and no closer to mature tree trunks than 20 to 30 cm (8-12 inches). As mulch decomposes, more should be added to maintain a depth of 5 to 7.5 cm (2-3 inches). Rather than actually removing mulch from the garden and perennials in spring, pull back the mulch to allow the soil to warm and once warm, pull the mulch back over the soil surface. Pull back leaf mulch from tulip and other areas with spring bulbs
Winter mulch, as described in “When to Remove Mulch From Perennials in Spring”, is a strategy to protect more vulnerable plants such as those which are borderline hardy in the Hardiness Zone in which they are planted. The depth of winter mulch is 10 cm (4 inches) and is applied after fall freeze to protect the plant roots from the freeze/thaw cycle of extreme fall and spring temperature swings which can damage their roots. Winter mulch should be removed when the period of hard freezes is over to prevent crown and root rot.
For further information on Mulch, please see:
Smart gardeners improve their soil and weed control with organic mulch
Problems With Over-Mulching Trees and Shrubs
Wishing you much success in renovating your gardens.