Certain scents are natural rat repellents

Q. Rats keep tunnelling in my compost heap. I have tried traps, but ants eat the bait while leaving the trap unsprung. Do you know of any baits that will attract rats and not ants — or anything else I could to keep rats out of the compost?

A. I live in a neighbourhood where rats have been a major issue in properties close to mine. Only once did I find a rat in a corner of one compost heap. It was at a time when a series of eye surgeries had left me in too much discomfort to dispose of kitchen vegetable and fruit trimmings in my usual, rat-proof way.

With that one exception, I have a longtime habit of digging kitchen organic waste into deep holes in the garden where extra moisture retention would be helpful. The materials decompose quickly, “on-site.”

Because post-surgery discomfort made it impossible for me, for a time, to dig those holes, I put the kitchen waste on a heap, covering it lightly with some of the compost. The next time I approached that heap, a rat scurried out of it.

I realize that not every garden setup allows for disposing of kitchen peelings and other compostable food waste items using my burying method. Other measures include using purchased rat-proof composters or enclosures made of solid wood or/and wire mesh.

Certain scents are natural rat repellents. Coffee grounds have the reputation of being repellent to rats and are fine for adding, in moderation, to compost heaps — in scant layers or distributed around the sides of a heap.

I use mint to keep rats and mice out of my garden shed. When I have an abundance of mint in the garden I place entire stems around the inner perimeter of the shed. In winter I use cotton balls infused with mint in essential oil form or in a less expensive, strongly mint-scented mouth wash.

Eucalyptus and citronella are more essential oils whose pungent odours tend to deter rats.