Horse Manure-be careful you don’t get more than you bargain for

I was going to condense this article for you all but have not had time, and I think the full article will be better for you all to read. It will certainly make you question where you get your horse poo from and what the horses were fed. A very eye opening read. ENJOY

Horse Manure-be careful you don’t get more than you bargain for

This is a great article taken from:-Town and Country Farmer. Jan/Feb 2016, Vol 33 No 1.
Article Written by Wayne Jeffery

I was going to condense this article for you all but have not had time, and I think the full article will be better for you all to read. It will certainly make you question where you get your horse poo from and what the horses were fed. A very eye opening read. ENJOY

Ever since Ian and I struck the first blow in our veggie patch adventure one of our main objectives has been to improve the soil quality. Almost every crop seems to thrive in nutrient rich, friable, well drained soil and when you start with a dry, rocky, dusty paddock you know it’s going to be a long haul.

Over the years we have worked hard on mulch collection and manure additions, especially in our poly tunnel glasshouse. This year we were particularly excited at the possibility of having home grown tomatoes as early as November. So can you imagine the sheer shock, frustration and anger that we felt on finding out that we have been inadvertently poisoning the very plants we are trying to nurture? Seriously! It turns out that the horse manure we have been collecting and mulching is laced with residual herbicides.

Now my gardening love affair with poo started way back on the family farm when dad and I used to clean out the neighbours chook sheds. We would shovel out the manure onto the trailer and then spread it around our apple trees. Dry, dusty, dirty work but great for the trees and at the right price!


Over the years the availability of chook poo has declined but around our area more and more properties seem to have bags of horse poo out. the front for sale. Ian and I arranged to leave a trailer at a nearby property and have it loaded with the mixture of rice hulls and horse manure when the stables were cleaned out. After a year of composting, how good would this stuff be for our soil? Tragically, we had never heard of Picloram or the Pyridne family of herbicides.

We had never heard of Clopyralid or Aminopyralid either. Nor nearly two hundred brand names of broad leaf herbicides.
Herbicides that can legally be used in hay and oat production. Herbicides that can end up in horse poo at levels lethal to a vast array of vegetables and flowering plants. Honestly, I can still barely believe it.

I was really keen to get our glasshouse tomatoes growing early this year. I purchased some advanced plants and planted them in beds freshly dug over with a healthy addition from our compost piles. Hard work but well worth it, or so I thought.

Growth was almost non existent. “Told you it was too early”, grumbled Ian. Gradually there was some growth but the plants became spindly with the leaves cupping and the tips curling. “Perhaps the rice hulls have leached all the nitrogen out”, mused Ian. “I knew we should have done a soil test”. Sadly, I knew it wasn’t just Ian being Captain Negator either. We also had plenty of other plants that weren’t flourishing.

As fate would have it I’d planted quite a decent patch of potatoes and filled the trenches primarily with our mulch. Rich, friable, well draining… Poison! The obviously mutated, twisted, fernlike growth of the potato leaves was the final pointer to our problem. So with that evidence and a lengthy stint giving google a solid workout the scope and impact of this residual herbicide problem has now become apparent.

If you search the internet yourself (clopyralid horse poo will give you a solid starting point) you will find accounts of the problem from numerous American states, the UK and here in Australia. Instances dating back ten years or more but still occurring today. For those of us who love our gardens there are many cases that make for sombre reading. Commercial composters selling tainted compost, small farmers losing their livelihood. I’m still wavering somewhere between outrage and depression at the situation.

I’ve added our compost to so many beds in the open paddock, no wonder the climbing beans are deformed and the peas were a waste of time.


These herbicides can still have an effect on certain plants at levels as low as one part per billion! Tomatoes and potatoes are particularly susceptible but the list also includes sunflowers, carrots, eggplants, peppers and many more.

Apparently most chemicals break down quickly in the composting process. Unfortunately Picloram, Clopyralid and Aminopyralid don’t. They are easily absorbed by unaffected plants (hay and oats) and remain chemically stable and intact through an animal’s digestive system and contaminate manure, urine and stable beds. Just imagine how much tainted urine our rice hulls have soaked up. Argh!

And what a crazy state of affairs. Sure the herbicide labels have a warning on them. Something along the lines of “Do not apply to crops that will be used for the production of compost or mulch. Such Compost or mulch made from treated plant material may cause damage to susceptible crops and plants!’ Great.
Where’s the warning on the hay? The oats? Or most importantly, the manure? What a nightmare.
Rectification of the problem has been hard, depressing work. And it’s not over yet.

All the soil in our glasshouse has now been wheelbarrowed out and replaced but throughout the patch there remains pockets of mulch, harbouring its toxins ready to nobble our next planting. Constant working of the soil is said to help leach the chemicals out but with the nasties operating at such tiny concentrations it’s hard to be optimistic.

I’m quite surprised that I’ve never come across this problem before. I’ve been warned about importing weeds to the garden by applying manures without composting them but not this disastrous situation.

Imagine how many people have been left scratching their heads wondering why their garden was struggling. I guess the best we can do is to warn others of the problem and source our manures carefully. If the horse owner doesn’t know the history of their horse feed then the manure just isn’t worth the risk. Believe me. We sure found out the hard way.