Stymie those un­wanted weeds

The Tribune (NZ) - - GARDENING - WALLY RICHARDS Prob­lems? Ring me at 0800 466464(Palmer­ston North 3570606)Email wal­lyjr@gar­de­ Web site www.gar­de­

Weeds tend to run ram­pant at this time of year.

An ef­fec­tive chem­i­cal-free way of keep­ing in­va­sive weeds un­der con­trol in open ar­eas of gar­den is by us­ing weed­mat.

A wo­ven plas­tic mat, weed­mat on the soil sur­face pro­vides a bar­rier to most weeds, with the ex­cep­tion of one or two types of grasses. Be­cause the mat is wo­ven, it al­lows mois­ture and some wa­ter-con­veyed plant foods to pass through to the soil below.

It also al­lows the soil to breathe, pre­vent­ing an anaer­o­bic sit­u­a­tion oc­cur­ring.

Pre weed­mat, sheets of black plas­tic film were laid down and were cov­ered with ma­te­rial such as sco­ria (red­dish volcanic rock). The soil un­der­neath be­came oxy­gen de­prived, and over time, the oxy­gen starved soil be­came anaer­o­bic, with any plants grow­ing in it even­tu­ally dy­ing. A great im­prove­ment on plas­tic film, weed­mat only works in one di­rec­tion, pre­vent­ing weeds from grow­ing up­wards.

It’s not a fool­proof so­lu­tion, how­ever. Weed seeds can ger­mi­nate in what­ever medium cov­ers the mat, and their roots will pen­e­trate the mat down­wards. The plus is that th­ese are easy to pull out as they can­not eas­ily es­tab­lish a se­cure root sys­tem.

Weeds will also ap­pear where the mat has been cut to al­low pre­ferred plants to grow. As it’s not al­ways easy to fit snugly around es­tab­lished plants, it may pay to over­lay cuts and holes with of­f­cuts to min­imise weed ger­mi­nat­ing op­por­tu­ni­ties.

Weed­mat is also re­mark­ably lon­glast­ing. Cov­ered with bark or stones to pre­vent ex­po­sure to UV, weed­mat could last in the gar­den for 25 years or more.

But do be care­ful about what you use to cover the mat. For­ag­ing birds will flick any lighter ma­te­rial off, so use bark nuggets (large bark pieces) or suit­able stones as cover.

For veg­etable and flower beds, how­ever, weed­mat is not so prac­ti­cal. So, to dis­cour­age weeds in th­ese plots, place lay­ered sheets of soaked news­pa­per or card­board on the soil and cover with a pur­chased (weed-free) compost.

This will cre­ate a tem­po­rary weed bar­rier while seedlings can be planted

di­rectly into the cov­er­ing compost.

There are plenty of ad­van­tages to us­ing card­board or news­pa­per as worms love it, mois­ture is re­tained bet­ter, and car­bon is re­turned to the soil.

For in­va­sive weeds such as con­volvu­lus or twitch (couch) grass peren­ni­ally com­ing through from next door, the only long-term so­lu­tion is to dig a trench along the fence line about 20 to 30 cm deep and line the fence side of the trench with sheets of gal­vanised iron. Back fill the trench so that the iron is buried deeply in the ground but pro­trud­ing a few cm above the soil level. Cap this with wood or old bricks to re­duce the chances of hands or feet be­ing cut on the ex­posed edge.

If you can’t get the iron flush with the fence, sim­ply pour salt into the gap when­ever a weed ap­pears. Salt is also an ex­cel­lent way to con­trol weeds grow­ing be­tween pavers or in cracks in drives or paths.


The white tri­umphant trum­pets of the pro­lific in­va­sive weed Con­volvu­lus ar­ven­sis. Con­trol is pos­si­ble in cer­tain cir­cum­stances.

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