Amending Soils with Manure [Building a Greenhouse: Part 3]

Posted by Chris Michael on May 1, 2013

 Building a greenhouse (Part 3)

This is our third video post in a series on "Building a Greenhouse," and today we're talking about soil amendments!

In Part 1, we showed you some of the best benefits of building a greenhouse including:

  • Extending your growing season
  • Gaining more control over your growing variables (pests, temperature, humidity, etc.)
  • Providing shelter for crops from snow, hail, and high winds

And in Part 2, we walked you through installing, securing and inflating your greenhouse covering.

If you're building a greenhouse for hydroponic production, you won't need soil amendments. See the Greenhouse Bundle for more info on building vertical hydroponic greenhouses.

If you plan on growing in the ground, then you will probably want soil amendments to get your soil to the ideal texture & nutrition levels for growing. Today, we'll be discussing some basic soil amendments you may need to do once you have your greenhouse cover on and your soil is fairly thawed out.

nate soil amendment hoophouse

Testing manure for salt content

Manure can be a great amendment for new soils. Soil that’s being worked for the first time will take around 2-3 inches of composted manure to till in -- the goal is to get your soil to a minimum of around 5% organic matter. Soil that has been worked before and has already been amended will take around 1 inch of composted manure each year.

One thing you have to be careful about is making sure your manure doesn't have too high a salt content. If you start to see salt accumulating on your soil surface or see salt accumulation on the manure itself, you know that the content is too high! If you are worried about salt in your manure, you can always have it tested by your local university lab, or by using an EC meter. If using an EC meter, manure can be diluted to a certain percentage with water (depending on the estimated inches of water to be applied during the growing season) and then measured.

I would try to stay away from manures that exceed 6.0 dS/m if possible. If manures test higher than this, then you know that if you are going to use them, then you must apply much more water to leach out some of the salts. If your soil has poor drainage, then this isn't possible, and you shouldn't use the manure. One thing that can be done if you are concerned about salts, is to use plastic mulch. This reduces evaporation from the soil surface and reduces the amount of salt buildup, or salt-pan that can accumulate in the upper portions of your soil.

Testing manure for herbicides

Herbicides are another major concern. Before buying manure, ask the supplier if any herbicides are used around the corrals, stalls, barns and outbuildings where the manure is collected.

If the answer is yes, then DO NOT USE THE MANURE.

It’s an unfortunate fact, but there are a number of herbicides that persist and can contaminate manure either because they were applied to the manure itself, or because they were applied to the hay used to feed the animals. For this reason, it’s very important to know whether herbicides were sprayed in the area where the manure was collected. If it was, do not use it.

It’s also important to ask the supplier whether the manure came from animals fed on grass hay that was treated with Tordon or Grazon. Both of these herbicides contain chemicals (aminopyralids) that last a long time and kill broad-leaf weeds. If either of these herbicides were used on the hay, the manure will kill your garden. As a side note, there are other “weed and feed” products and herbicides used on lawns that will do the same, so be careful with composting grass clippings from treated lawns.

Manure can often be tested for herbicides by labs, but these tests are expensive and aren’t always sensitive enough. Fortunately there’s a way to test manure yourself.

It’s called a bioassay. It’s very easy to do. Essentially you just take a number of samples and see if plants planted in those samples show signs of herbicide damage. For complete instructions, check out this document.

Types of manure

There are many types of manure, and they all have different qualities. Remember that all manures should be composted before they are used.

Manure from horses and cattle are the most common types of manure available, and when composted, are high in organic matter. Sheep and goat manure is usually of excellent quality, often having less salt content than horse or cow manure. Poultry manure is very hot when it is fresh, and even when composted can be too nitrogen-rich. Use it with caution, and if it’s still hot after composting, make sure to incorporate carbon rich organic matter with it (i.e. straw, sawdust, etc.) to keep the effects of the nitrogen under control.Chris till soil

Other Soil Amendments

There are many other soil amendments that can be used instead of, or in conjunction with manure. But that is for another post. For the beginning gardener, amending soils with manure is a great start. If you can start with manure, you can graduate on to other things.

So start here, and we’ll do our best to help explain other amendments as time goes on. 

Watch the video:

Getting ready to build a greenhouse? Check out this post on planning and heating a greenhouse. If you still have questions, contact us and we'll help you with planning.


Topics: Greenhouse

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