Mittleider grow box maintenance needs to be completed once or twice a year. Grow boxes in a Mittleider garden are filled with sand and sawdust. As the gardening season progresses the sawdust will decompose. As it decomposes the growing medium in the grow box drops. The lost material will need to be replaced.
How often to add more sawdust
Here on our little homestead we will do Mittleider grow box maintenance at before each gardening season right before planting. In grow boxes where we rotate in a new crop for our fall gardens the grow box will get topped off a second time. There are a couple things to consider when deciding how often to add more sawdust.
What to consider when deciding when top off a grow box
Performing mid season Mittleider grow box maintenance on crops like kale or tomatoes would be a problem because the fruit and growing tip wouldn’t get buried with the added sawdust. To try and top off a bed with crops such as cabbage or spinach you would end up partially burying your crop.
A common side effect of adding fresh sawdust is a drop in available nitrogen. Watch for nitrogen deficiencies if topping of the grow box during the growing season. If you see symptoms of a lack of nitrogen you will need to correct for nitrogen deficiency. Urea is a common nitrogen source that is widely available.
What sawdust will work
A common question I see asked is what type of sawdust is correct to use and what size it should be. The type is easy, anything but walnut sawdust will work. Walnut contains tannin that will kill seedlings and severally stunt the growth of established plants. Avoid any sawdust that could possibly contain walnut.
The size of the sawdust is important. Anything too large, or too small, can cause serious problems in your Mittleider grow box. See my blog entry on identifying the correct sawdust size. Another acceptable source of sawdust that can be bought is from equine pellets. Equine pellets cost around $6 per 40 pound bag and will roughly triple in volume once wet,
Mittleider grow box maintenance in our potato box
In this video you will see our potato and sweet potato grow box. Because of the length of the sweet potato growing season this box is only filled once a year. It gets topped off right before we transplant the sweet potatoes.
If you cant find a good source locally you can use equine pellets sawdust. In a Mittleider garden the sawdust is used to fill seedling flats or even entire grow boxes.
Ideally you would have access to free sawdust from a sawmill and don’t need to go through the added expense of buying sawdust. If you’re only going to start seedlings a single bag of pellets would last a long time. It also wouldn’t be cost prohibitive. To fill grow boxes would take a lot more sawdust and would quickly become expensive.
If you are considering using equine pellets sawdust to fill a grow box I’d highly recommend that you consider soil beds. They can grow food equally well despite your soil condition while being much cheaper.
How to go from pellets to sawdust
The process of taking pellets and turning them into usable sawdust is easy. All you need to do is add water with a good watering wand to soak everything well. As the pellets absorb water they will expand as the binding agent used a glue dissolves.
adding the pellets to a container that will allow the excess water to drain will make the entire process easier for you. Our wheel barrow has a crack and allows excess water to escape.
If you do not have a container that will allow water to escape try adding water a little at a time until all the pellets are damp. Try turning the pellets with a shovel to ensure everything is wet.
Where and what pellets to get
As the name implies, these pellets can be bought at business catering to horse people. Another source is at business that sell hardwood pellets for homes heated with pellet stoves. Those hardwood pellets are fine and any wood type except walnut will work. The pellet stove pellets can be bought in bulk and can often be bought cheaper by the bag than equine pellets.
The hardwood pellets intended for heating homes is often only carried seasonally and may not always be available. They may also be bought at discount in the spring as they’re no longer needed.
Watch sawdust being made with equine pellets
In this video you can watch equine pellets expand roughly three times into sawdust once it becomes wet. The process is quick and only takes a few minutes.
When it comes to gardening in grow boxes in your Mittleider garden it is extremely important to choose and obtain the correct sawdust. Not just any sawdust will work as your Mittleider garden sawdust.
Most any type of tree will work, with the exception of black walnut. Black walnut has toxins in it called juglone that can stunt, deform or even kill other plants. If the sawmill cuts black walnut you should avoid that sawdust, even if it is free. Do nut use walnut for your Mittleider garden sawdust for any reason.
The only kind of sawmill that you should consider as a good source of sawdust is one that runs a large diameter circular saw blade. The blade kerf is wide enough that you will get the correct size of sawdust particles. See the video at the bottom of this post to see the correct size and an example of a sawdust that is far too fine.
Band saw sawmills
Sawmills that run band saw sawmills are becoming popular and can be found on homesteads where folks make their own lumber. Unfortunately the kerf is much smaller on these types of mills and the sawdust particles are too fine for our purposes and isn’t a good source for our Mittleider garden sawdust.
The size of the sawdust particles is important
Have sawdust that is too large, such as wood chips, will result in poor drainage and souring of your growing medium. This can prevent water from getting to our plant roots and even cut off oxygen. Either can surely kill your plants. (Remember the 6 laws of plant growth?) Planers or even wood chippers would be a common source of wood chips that are too large.
Just as too large can kill your plants, so can sawdust particles which are too fine. This sawdust is would be collected from table saws, band saws, and that cool saw you see in stores like Home Depot and Lowe’s. This sawdust is far too fine and can cause compaction. Once hard and compacted your plants can struggle to get water and nutrients. This fine sawdust is often free, but it can cause real problems in your garden and needs to be avoided.
What if there are no sawmills near me?
If you’re unable to locate sawmills near you and are determined to grow in sand and sawdust then you can buy equine pellets. When the pellets become wet they turn into a usable pine sawdust that works well. It takes just a few minutes to transform the pellets into a usable sawdust.
Is gardening in sawdust possible? Can you grow a garden in sawdust even though it has zero nutrients for the plants? You can with the Mittleider gardening method and it will do amazingly well. Sawdust generally has a nearly ideal pH, it doesn’t have any plant borne diseases like blight in it and can be acquired cheaply or even for FREE as we have done.
You need more than just sawdust
Unfortunately you do need more than just sawdust to grow a beautiful garden. First off, you will need to mix sand in with your sawdust. This will allow for proper drainage.
Because there is no nutritional value to the sawdust and sand it is therefore necessary that we add preplant and weekly feed to our custom soil mix. Due to no nutrients being in sawdust we must add them. As the result of giving the plants all the nutrients they need you will see them thrive.
To learn more about the Mittleider gardening method
We use sawdust in our Mittleider garden for our grow boxes and in our seedling trays. Each year we top off the grow boxes before the growing season begins. Today we made the trip over to a nearby town where a sawmill allows us to shovel our own sawdust for free. They make pallets and are largely cutting inexpensive cottonwood trees for the lumber. Any tree expect the black walnut provides a usable sawdust for a Mittleider grow box or seedling trays. Make sure you get the correct size particles in your sawdust! If you don’t have sawmills near you then you can use equine pellets.
The sawdust is mixed with sand for both the grow boxes and the seedling trays. For the grow boxes it is mixed at 3 parts sawdust and 1 part sand. For the seedling trays it is 2 parts sawdust to one of the sand. Both are mixed by volume. I’ll try and take some pictures that show the size of the particles. Too large and too fine are both bad.
No idea how much wood they cut in a week, but this sawdust pile is massive, the picture truly doesn’t do it justice.
We needed sawdust to fill our grow boxes and made a quick trip to Jamesport, MO to a sawmill. This lumber mill makes pallets and will allow us to take the sawdust for FREE. We just needed to bring a shovel and fill the truck ourselves.
They do not make pallets from walnut so this sawdust is safe to use. They have huge piles of excess sawdust and were happy to have us take some away. We will make a few trips here in the near future.
What sawdust is safe for grow boxes?
Any sawdust made from trees of any variety in the United States except walnut is safe for use in your garden. Walnut sawdust contains tannic which can retard the growth or even kill it if the concentration is high enough. If the sawdust has any walnut in it you shouldn’t use it.
Can you use sawdust from plywood?
There are two reasons you should not consider using sawdust from cabinet shops. The glues used in the process of making plywood can be toxic to plants and humans.
The second reason you shouldn’t use that sawdust from cabinet shows is that the particles likely either too large or too small for use in your garden. If they come from a planer then they will be too large to permit proper drainage and will sour in your garden.
Sawdust made on table saws, radial arm saws or with handheld saws is too fine. Sawdust that is too fine doesn’t drain easily and can result in compacting. If your growing medium is compacted the plants can’t get water or oxygen to their roots and will die.
How to pick the right sawdust for your Mittleider garden
If you would like to see how to determine what sawdust will work in your Mittleider garden be sure to read this blog post. There is even a video showing you the correct size and sawdust that will cause compaction.
But to put it plainly, sawdust from any source that isn’t a sawmill running a large circular saw isn’t going to work.
Can’t find a sawmill?
If you can’t find a sawmill locally that has the correct sawdust you can use wood pellets. Pellets that used for heating work as do equine pellets. For more information check out the blog entry on equine pellet sawdust.
Our quest to be self reliant and grow a healthy garden