Have you planted a green manure crop this year?

A few weeks ago we recommended planting a green manure crop as one of the fastest and easiest ways to improve your soil before you plant fruit trees. This week we’re showing you what the crop should be looking like by by now, and what to look for.

A green manure is a fast-growing crop of (usually) annual plants, and it’s one of the quickest ways to improve soil fertility and add organic matter to your soil.

The last couple of times we’ve planted new orchards, we’ve first put in a green manure crop before we’ve planted the fruit trees because we’re always aiming to increase the biodiversity under our fruit trees—it’s one of the best ways we can provide the right habitat for useful insects that help us keep the pests under control.

Sas planting a green manure crop in the nursery
Sas planting a green manure crop in the nursery

This year we planted a green manure in the block where we’ll be planting the new nursery in winter. The seed mix included grasses, legumes (nitrogen fixers) and herbs – grasses to add bulk organic matter to the soil, the legumes to add nitrogen, and the herbs to add a diverse mix of nutrients. If you’re not sure what seed to choose, you can check out our recommended plant lists (and even some suppliers of organic seed, if you’re in Australia) in this short course.

We’re always aiming to increase the biodiversity in our soil – it’s one of the best ways we can provide healthy soil to grow trees, as well as habitat for useful insects that help us keep the pests under control.

The more diversity you can get into your garden, the healthier your fruit trees (and all your other plants) will be. And if you’re growing your own food, you definitely want that food to be as healthy and nutrient rich as possible.

Clover starting to grow
Clover starting to grow

It’s always a good sign to see lots of clover seedlings coming up. We particularly like having clover because it’s a nitrogen fixer (taking nitrogen from the air and putting it in the soil where the trees can use it).

Clover is quite spreading and so out-competes less useful weeds, and it self-seeds so it will persist in the orchard for years.

Experience has shown us that even though we plough green manure crops back into the soil before we plant the trees, plenty of clover seedlings will still come up, and over time it will gradually spread throughout the orchard floor.

A bean plant in the green manure crop starting to grow
A bean plant in the green manure crop starting to grow

Before we plant the new nursery in July, we’ll be turning the crop in. We use a rotary hoe, or the disc behind the tractor, but in a home garden you can either turn it in with a shovel, or just mow it and leave it on the soil – it’s not quite as good, but the worms will eventually take that lovely organic matter underground for you.

Getting ready to plant a new tree
Getting ready to plant a new tree

One of the unfortunate consequences of using large macinery like a disc is that disturbing the soil so comprehensively provides the perfect environment for opportunistic weeds such as capeweed (below).

Beautiful but unpopular capeweed
Beautiful but unpopular capeweed

We appreciate all our weeds, and even the much-despised capeweed has many fine qualities, but it’s not the plant we prefer to see in the orchard, as it tends to out-compete more useful plants, without conferring the benefits of a nitrogen-fixer.

Just one word of warning – if you are going to turn in your green manure crop, try to leave at least a couple of weeks between doing so and planting your trees, because the rotting green material can become quite hot as it breaks down, and you don’t want to burn the roots of your baby trees!

So in a classic case of “do what we say, not what we do”, here’s our top 4 tips for looking after your soil when you plant your fruit trees:

  1. Plant a green manure crop
  2. Turn it into the soil at the site where you are going to plant a tree, preferably a few weeks before you plant
  3. Disturb the soil as little as possible when planting the tree
  4. Re-seed the area with preferred understorey plants.

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!