Herbs to Repel Insect Pests

Herbs to Discourage Insects

I have been whinging on for some years now, about the red ants in my poly-tunnel, the damage they cause and the seeming impossibility of eradicating them.

Baited ant traps were useless ‘be sure to put them on the paths that the ants take’ the directions advised. It seems the ants are attracted to the bait, taking it back to the nest where it annihilates all members of the colony. I followed all the instructions carefully - the ants built their nests under the ant traps and the colonies grew stronger.

I used Py solution – a pyrethrin based insecticide [and therefore organic]. This was okay although I had to dig up the nests and make sure the solution made contact with every ant – time consuming and not totally effective.

A friend advised me to use Eraza Ant Killing Solution [not organic – I was getting desperate!]. Well it also only worked on direct contact with the ants and where I used it inside [the poly-tunnel] it affected my breathing most unpleasantly.

I have just finished harvesting my lavender – a wonderful crop this year – and I actually managed to harvest it at the right time and in the best conditions for saving and using. I have bundles of it hanging in every room in my house for drying but, also to keep flies away, usually quite a pest in our rare warm, dry summers and this summer is definitely dry. Lavender is definitely one of my favourite herbs and though it can be used in cooking, I don’t. I use it for sleep cushions [it is so relaxing], in my wardrobes, cupboards and drawers to deter moths but it is also useful, especially in summer months when windows and doors are open, for repelling mosquitoes, moths and midges as well as flies. It has a reputation also, of helping to keep fleas off cats and dogs though, I’m not sure it would deter the very determined species I have in my area nor could I see my cats sitting happily while I rubbed lavender oil into their fur.

As I was preparing the lavender I wondered how other herbs might be used to discourage ants from my poly-tunnel or even from my allotment – a big ask!

Interestingly, cedar is really excellent for deterring moths. Clothes or household linens, stored in cedar cupboards or chests are most unlikely to be attacked by moths. If, like me, you would find the cedar furniture rather too expensive, it is possible to buy blocks of cedar wood to hang in cupboards. When the strong cedar resin aroma has faded, sand off the outside of the block to revive it for another few months.

Bay – laurus nobilis. I planted a small bay tree in a pot in my garden some years ago thinking that, as it was an expensive tree, I would be able to take it with me if I moved house. It is now 6 feet high and a significant shrub. It’s still in its pot but, I suspect, it has rooted through the bottom of the pot into the ground beneath. It is much too healthy looking to be a pot-grown bush. [I had a similar issue with a giant redwood tree –sequoia gigantium - given to me as a present some years ago as a 10in high sapling. I knew better than to plant it in my garden so I put it into a fairly substantial pot. However, a few years on it had grown 20ft high and was much too happy to be surviving in just a pot. I had to cut it down but, still haven’t managed to release the pot from the considerable root system underneath.]

Bunches of bay, fresh or dried will deter moths, cockroaches and flies. Try scattering the leaves in drawers and cupboard shelves.

Basil – excellent for keeping flies and mosquitoes away. Unfortunately, in the UK, this is not an outdoor plant and is not too happy indoors during the winter. While I do grow my own during the spring and summer months, for the rest of the year I will buy the pots from the supermarket. Pots of fresh bay are not only an essential culinary ingredient but are an excellent insect repellent.

Mint – now this herb would definitely keep ants out of my poly-tunnel if I planted it in there. Unfortunately, it would take over in one short season. I had started growing mint in my garden in an old Belfast sink but I found that I had to replant every year as it became pot bound quite quickly. I took a couple of small roots to my allotment where it quickly colonised an extensive area in that part of the allotment I had set aside for fruit trees and herbs. It is a magnificent display each year but requires assertive, if not aggressive weeding out each year to keep it under control and away from my fruit trees. However, while there are ants nests on all other parts of my allotment, there are none in that area. I might consider pots of mint placed on the path of the poly-tunnel for next year.

There are very many varieties of mint and while I have tried a few of them I now grow just spearmint and apple mint both of which would be among the Classic mint group. Mint is useful for discouraging flies, fleas, mice, ants and mosquitoes.

Rosemary – every home should have some and although I don’t use a huge amount in cooking, it is not a herb I can do without in my kitchen and as it is available all year round it is useful to have a pot or two outside the kitchen door.

Rosemary can grow into quite large shrubs or even hedges and is wonderfully aromatic when you brush against it. I have always grown mine in large tubs and my favourite is the prostrate variety which hangs down over the edges of a large ornamental tub in my back yard.

Three or four years ago I took cuttings from my quite ancient prostrate rosemary and the other one I was growing a Tuscan Blue. I planted a couple of new little bushes from these cuttings in my neighbour’s garden and the rest in pots for my own use. We had a particularly harsh winter that year and I lost all of my rosemary plants, including the really old one in the tub. The frost had been so hard it had frozen right through to the roots of the potted plants. My neighbour’s – planted straight into the garden - had survived. I thought I would have no trouble replacing what is, after all, a fairly common herb but garden centres and several nurseries had also lost their stocks of rosemary in the same way.

Rosemary has a reputation of keeping mosquitoes and cats away. However, I have four cats and while I certainly don’t see them lazing under the rosemary pots, nor does it keep them out of my yard.

While I don’t grow Tansy as I have no culinary use for it – the leaves are very bitter. It is an old deterrent to ants, mice, moths and animal fleas.