Soil prep before tree planting

It’s time to do some soil preparation before you plant your fruit trees.

Lush green manure crop
Lush green manure crop

It’s a great idea, if you have time, to plant an autumn green manure crop. This is particularly important if:

  1. you have poor soil
  2. you don’t have enough topsoil
  3. you’re planting a tree into an area where a tree has died or you’re aware there has been disease, or
  4. you’re keen to give your new trees the best possible start in life.
Clover is a great addition to a green manure mix
Clover is a great addition to a green manure mix

Here’s how to do it. You can either buy a green manure mix, or make your own—you can find both autumn and spring plant lists in our short course Build Soil Fertility with Green Manures.

We buy the seeds separately and mix them together in a bucket before sowing. You can also add some fine sand into the mix to help spread it evenly.

Mix the seed well before sowing
Mix the seed well before sowing

It’s a good idea to lightly work the soil up (by machine or digging with a shovel) before you spread the seed, then rake lightly to cover the seed with a fine layer of soil.

The idea is that you wait until the ‘autumn break’ before you plant, i.e., after the first decent rainfall event that signals the end of the summer dry. Depending on your area and climate, hopefully this has already happened and you’ll get enough natural rainfall for the crop to grow. 

If you live in a particularly dry area or are currently experiencing drought, it’s still worth trying to get a green manure crop started, but it’s only really practical to do this on a small area, because you’ll have to irrigate the crop to get any benefit.

Select your tree sites first, and then work the soil and plant the green manure crop in an area at least 1 square metre at each tree site.

Once the crop has grown (ideally to at least a few inches tall), turn it back into the soil. It’s good to do this a few weeks before you plant your fruit trees, to give the green matter a chance to break down in the soil.

It’s a pretty straighforward practice, but the benefits to the soil are enormous. If you use the right mix of seed you should be adding a wonderful nutritional boost, as well as some bulk material to increase the organic content of your soil and provide lots of lovely food for the soil microbes.

What to do with prunings?

We’ve been busily pruning apricot trees this week, making the most of this beautiful autumn weather and enjoying the glorious colours.

If your apricot tree is like ours, with a spot of gummosis, then it’s very important to pick the diseased prunings up and dispose of them properly to help prevent disease next year.

The best way is to return them to the soil somehow. Large animals (sheep, goats, horses) just love to eat prunings (especially if they still have green leaves on them), and will often break them down enough to put the remains straight into a compost pile.

Now that we have Tessa’s in-house micro-dairy here on the farm as part of the Harcourt Organic Farming Co-op, the prunings go straight to a bunch of cows who think fruit tree prunings are a high treat!

Another great technique is to chip the prunings. You can either leave them in a pile to age and then put them back on the trees, or put them into a compost pile. Learning how to make your own compost is one of the “must-have” techniques for all gardeners that are serious about growing their own food. It’s really hard to find good quality compost to buy (not to mention quite expensive, as it’s something you need to apply regularly), plus it’s one of the best ways to capture the nutrients from your garden ‘waste’ and return them to the soil. If compost-making is still a mystery (or keeps going wrong), our Compost That Works online short course will get you on the right path.

Larger prunings also make good kindling or firewood, or can be turned into biochar using one of the techniques we’ve described in other blogs, so there’s really no need to waste anything!

Biochar in a bathtub

We became big fans of biochar years ago when we went to this workshop, and we’ve also written about it here. We even held our own workshop on the farm to learn how to make biochar vessels out of 44 gallon drums.

The bathtub biochar method in action
The bathtub biochar method in action

Despite all of that, we’ve never made it ourselves, because it seems like a lot of effort to produce a small amount of biochar.

That may all have changed! We were lucky enough to go to a small, privately run workshop recently that introduced us to a much simpler system for making biochar in a bathtub.

It was hosted for us by Grow Great Fruit members Win Westerhoff (below left) and Clare Claydon, and the workshop was run by Jim Sansom (below right), who started by talking us through the main steps of the method.

Jim Sansom explaining the bathtub method
Jim Sansom explaining the bathtub method

The bathtub method is based on the ‘Kontiki Cone Kiln’, which is a large (about 1.6 m across) kiln for making biochar, but is a much simplified version.

One of the challenges with this method is that there’s no hard and fast rules about when to stop the burn. “Judge when to stop” was Jim’s advice, “when a stick has lost its identity as a stick”.

Another thing to know before you start is don’t use a cast iron bathtub, or it may crack when you light a fire in it. And obviously don’t use a modern plastic or fibreglass bath either – you need to find an old steel bath at your local tip shop.

At the workshop we went through the actual process of making biochar under the expert tutelage of Jim, Clare and Win — and it wa:s surprisingly fast and easy.

Here’s how it works:

Step 1 – Fill the bottom of the bathtub with light, dry fuel.

Starting the fire in the bottom of the bath with light, dry material (and a bit of metho if needed!)
Starting the fire in the bottom of the bath with light, dry material (and a bit of metho if needed!)

Step 2 – Light it on fire. (Pro tip: use a bit of metho if needed). Aim to get a good strong fire going along the whole length of the bathtub.

Step 3 – Once it’s burning, pile up with bigger stuff, but make sure it’s burning the whole length underneath. (Pro tip: this is much easier on a still day than a windy one.)

Step 4 – Stack the bath until it’s 3/4 full. If the fire is burning well, it shouldn’t be too smoky. It’s fine to use bigger wood in the bathtub as long as it’s all roughly the same size so it burns at about the same rate.

Hugh keeping the fire going evenly along the whole bathtub with a rake
Hugh keeping the fire going evenly along the whole bathtub with a rake

Step 5 – Use a metal rake to pack the wood down hard, and to keep the fire burning evenly and everything burning at the same rate. The gases will be pushed out of the wood and are then burned in the bathtub, which prevents oxygen getting down into the fire. If too much oxygen gets into the fire the wood will just burn away to ash. New research has shown that if the biochar is made at a lower temperature you end up with biochar that has a higher level of organic matter.

Hosing the bath to put the fire out when you judge it's finished
Hosing the bath to put the fire out when you judge it’s finished

Step 6 – When you judge that most of the material is blackened to char, quench the whole thing with a hose.

Hugh and Clare admiring the finished product
Hugh and Clare admiring the finished product

It’s OK for sand, dirt, clay and mud to be on the wood and in the cooking process, and in fact this may be beneficial by creating a more highly mineralised final product.

How do you apply the finished product? We’ve covered this before in other blogs, but here’s the methods that Clare and Win use:

  • dig a trench, tip in a barrow load of biochar, add compost and a scattering of blood and bone;
  • broadacre – spread with a fertiliser spreader and then go over it with harrows.

The point is finding some way to incorporate biochar into your soil where it will work its magic.

Of course it’s not magic, it’s science! Biochar has remarkable effects in soil by providing both a stable form of soil carbon, and by providing amazing (and extensive) habitat for soil microbes. If you still need convincing of just what an awesome impact this can have on your soil, you may want to take our Soil Biology and the Soil Food Web short course.