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.
Why I don’t like a 4 foot grow boxes in a Mittleider garden
I’ll be honest here, I don’t like 4 foot wide grow boxes. They’re popular and you will see all kinds of articles and videos where they are recommended. They require too much bending over of the gardener for my liking. For a Mittleider garden I think they’re generally a mistake.
It is difficult to tend to stuff in it and you can’t reach from one side to the other. This becomes particularly evident when things are grown vertically. Reaching towards the middle of the box to prune or harvest from a mature plant is near impossible. Sure, you can push through and get it done but you risk damaging plants. you could even knock off nearly ripe vegetables.
The top of these tomatoes in the picture below are a little more than 3 feet apart. I can only prune and harvest easily by going down each side of my grow box. Growing these tomatoes in a 4 foot wide grow box would prevent the easy access necessary to properly care for our plants.
Are there good uses for 4 foot grow boxes?
There are indeed. First, if you’re on a very tight budget yet determined to have a grow box the wide grow boxes will work. For the cost of two 18 inch wide boxes you can build one 4 foot box. But if you’re on a budget I’d highly recommend growing in your own soil.
The only time I might recommend a 4 foot wide grow box in a Mittleider garden is for growing potatoes. We have heavy clay soil here in Missouri. Our grow box dedicated to growing potatoes allows them to sprawl and makes harvest a breeze. It is isolated from the rest of the garden and is used only for potatoes. In this picture below we grew sweet potatoes last year.
What size grow box do I prefer?
That’s easy. An 18 inch wide grow box is ideal, particularity for vertical crops in my Mittleider garden. We built these grow boxes in our in the garden green house.
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.
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.
After receiving a good hard frost we decided to dig up our Georgia Jet sweet potatoes. We are tickled with our harvest that ended up filling a wheel barrow. Not sure what the total weight as we just didn’t weigh them.
They were growing in a 4 foot wide and 15 foot long grow box that was filled with a mixture of sand and sawdust. Digging them was very easy, we used only our hands to sweep the sand and sawdust out of the way to expose the sweet potatoes.
You can see the outline of the growbox in the picture below. As you can see, they grew like mad. Next year I will prune the vines as they grow beyond the box.
This was the average size of what we harvested. They grew easily in our sand and sawdust and weren’t mishappen.
This is the completed harvest here in the wheel barrow. Not a bad haul for a 4 x 15 foot growing area!
We now have 32 Georgia Jets sweet potato slips in our 4′ X 15′ grow box. I’ve never knowingly eaten one before but wanted to give them a try. This is also our first year growing any sweet potato in a grow box with a sand and sawdust growing medium. Last year digging potatoes in the heavy clay soil was a lot like work. This year it should be so easy.
I’m still working on clearing the grass and weeds around the grow box. When finished there will be a bare dirt border 5 feet from the box. By doing this it helps keep insects away from our vegetables. It also helps keep weeds from getting into the grow box and competitimg with the vegetables for the water and fertilizers as well as space and light.
With the grow boxes filled with medium and seedlings transplanted our next project was the completion of the automated watering system. Lesson 16 in the MGC book, page 125, covers the construction details of the automated watering system. Three holes were drilled every 4 inches of the 3/4 inch schedule 30 pvc pipe to water our grow box. The holes are small, we ordered the number 57 drill bit from Amazon as our local stores don’t carry anything so small.
The holes are positioned to get a stream of water to squirt straight down into the bed and the other two at an angle towards the outside of the box. Our system will be drained in the winter as it turns cold. For all the piping that is below ground we elected to go with schedule 40 to help ensure we don’t have to dig up a broken pipe.
Currently we water by connecting a garden hose to the system. At some point we may go high tech and use a truly automated system.
These 30 foot long and 18 inch wide boxes are being built for our fall crops. We will also be building an in garden green house over these boxes. This will allow us to extend our growing season by 12 weeks.
Once construction is complete they will be filled with a mix of sand and sawdust as our growing medium. As that growing medium contains no nutrients for the plants we will be providing all of the necessary nutrients via an inexpensive mix that is applied on a weekly basis.
The PVC you see next to the treated 2×8 serve a few purposes. They help hold the boxes level and in place once filled with our sawdust and sand growing medium. They also support the a-frames we will be making by heating and bending some half inch pvc. Once the mini a-frames are in place they can then be covered with green house plastic to protect our fall crops.
Next to the grow boxes you can see our sweet potatoes growing like mad.
Our quest to be self reliant and grow a healthy garden