Thinning to protect your tree

As part of our continuing series about fruit thinning (a very relevant topic in spring) this week we’ll talk about the second main reason we do thinning, which is to protect the structure of our trees.

A broken lateral in an apricot tree caused by to much fruit (or not enough thinning)
A broken lateral in an apricot tree caused by to much fruit (or not enough thinning)

Most fruit is carried on the small side shoots, or laterals, that grow from the main branches — they are a very precious part of the tree, and need to be protected. Left to its own devices, the tree will frequently set so much fruit on a branch or lateral that the weight of the fruit breaks the branch, as you can see in the photos above and below.

Too much weight has broken branches in this apple tree
Too much weight has broken branches in this apple tree

Our job when thinning is to remove some of the fruit that the tree has set, leaving only as much as any structural part of the tree can easily carry.

Bebeco apricots after thinining - not too much weight for the lateral to carry
Bebeco apricots after thinining – not too much weight for the lateral to carry

It’s important to imagine how large and heavy the fruit will be when it’s fully mature – as a very rough rule of thumb, a short lateral can only bear the weight of one piece of fruit, and a longer or stronger lateral can carry two or more pieces.

Tatura 211 peach after thinning - just one peach on the lateral
Tatura 211 peach after thinning – just one peach on the lateral

Of course the actual amount of fruit you can leave on the tree depends on many variables:

  • the type of fruit,
  • the variety (cultivar),
  • the ultimate size of the fruit at harvest,
  • whether the tree is heavy, medium or light crop,
  • when it’s due to be harvested,
  • age of the tree, etc.

It’s fine to just follow the rule-of-thumb guidelines we provide, or if you’re keen to protect your tree and in a hurry to get good results you can use the charts we’ve developed in the Grow Great Fruit program and the Fruit Tree Thinning short course to save yourself a few years of trial and error!

Rude fruit

Have you seen any double fruit in your fruit trees?

A double cherry
A double cherry

It’s relatively common to see double fruit (like these cherries), and as you can see, in many cases the fruit is still perfectly usable.

The photo below shows a particularly unusual one that has caused the stem to split, but doubles – or conjoined fruit – are not an uncommon occurrence, particularly in stone fruit.

Conjoined apricots with a single stem
Conjoined apricots with a single stem

Some varieties (like Angelina) seem particularly prone to this, and are often a good demonstration of the phenomenon where one piece of fruit dominates the other and ends up much larger.

Conjoined Angelina plums where one plum is much bigger than the other
Conjoined Angelina plums where one plum is much bigger than the other

In many cases one of the pieces of fruit ends up so small as to really be un-usable, or the skin of the fruits are torn when separating them, which of course downgrades the quality of the fruit.

A rude Angelina
A rude Angelina

And sometimes the extra piece of fruit is so small as to be insignificant, and sometimes can be removed without doing damage to the main fruit. But they’re also often cute, funny or downright rude, so why would you?

So, what causes this, and is it avoidable?

Whether a fruit will be double or not is determined the summer before, when the fruit buds are developing.

If the young buds go through heat or water stress during the summer months, this increases the development of doubled fruit.

There’s not much we can do about heat waves, particularly with climate change affecting our environment so quickly, but we can make sure our trees are adequately irrigated, particularly during a heat wave, to minimise the stress on the tree.

Irregular or inadequate watering can also be one of the causes for fruit splitting, which is another whole story but can look like this.

A green nectarine with a split in it, possibly caused by irregular waterin
A green nectarine with a split in it, possibly caused by irregular watering

In a home garden it’s not terribly important whether you have double fruit or not because it’s usually still usable, but it’s not as pretty, and now you know how to avoid it! Download Smart Irrigation for Fruit Trees for more tips about how to irrigate wisely without wasting water or money.

How do you plant a green manure?

We talk about green manures and how important they are for the soil all the time, but the logistics of getting the seed into the ground can be daunting, especially on a large scale, so we decided to share how we did it this week in the nursery.

The fallow nursery block after the disc plough has been used to turned in the weeds
The fallow nursery block after the disc plough has been used to turned in the weeds

Carr’s Organic Fruit Tree Nursery is made up of three different blocks, and at any given time one of them is fallow.

This is the perfect time to plant a green manure crop to restore soil fertility,
replenish the soil, and replace the organic matter we’ve removed by growing and harvesting hundreds of fruit trees.

After hearing soil scientist Dr. Christine Jones a couple of weeks ago and learning more about the importance of multi-species groundcovers, we got inspired to ramp up our green manure seed mix even more than usual. More on that in a moment, but first, how do you actually prepare the soil?

We’re lucky enough to have equipment, so Hugh jumped on the tractor and first up used the disc plough to turn in the weeds that were already growing. You can see the result in the first photo above.

Those weeds were in effect the first green manure crop, which we’re now following up with a more diverse plant mix that will hopefully stay green over summer.

We’re always wary about using equipment like discs, harrows or rotary hoes because of the way they smash up the soil and can damage microbes, particularly soil fungi.

But you’ve also got to find a way of getting the seed into the soil, and Dr. Jones was very much of the opinion that it’s worth disrupting the soil (albeit as minimally and infrequently as possible) to get diverse, perennial groundcover crops established. The benefit should quickly outweigh the initial cost.

The disc did a good job of turning most of the weeds in, but it was still too rough for the seeds to connect with the soil well enough, so next we put on the rotary hoe.

Hugh using the rotary hoe to prepare the soil for the green manure seed
Hugh using the rotary hoe to prepare the soil for the green manure seed

You can see the difference just one pass with the rotary hoe makes (on the left hand side of the photo above). It’s still not a super smooth seed bed, but it’s good enough for the seeds to hit the soil when they’re broadcast, rather than getting stuck on a clump of grass – where they definitely wouldn’t germinate and grow!

If we had seed-drilling equipment that could inject the seed straight into the soil we wouldn’t need to do this step, and in fact many innovative regenerative farmers are sowing seeds directly into pasture these days, with no soil disturbance of loss of ground cover at all, and getting excellent results.

The green manure seed mix spread on the soil
The green manure seed mix spread on the soil

But needs must, so the next step is broadcasting the seed by hand. It’s always a challenge to scatter the seed evenly over a patch this size, but by dividing the patch into sections and weighing out portions of the seed mix we got a pretty even spread.

The last step is raking the whole patch to get a light cover of soil over the seeds, and finally give the whole patch a really good watering in.

Raking the seeds to get a light cover of soil over them
Raking the seeds to get a light cover of soil over them

We’ve always used a fairly diverse mix of seeds for the green manure, but this year we went nuts! We were also influenced by Dr. Jones to make a couple of other modifications – we mixed in a good dose of worm castings out of our worm farm, and then we soaked the seeds in raw whey (sourced of course from Sellar Farmhouse Creamery) for a couple of hours before we sowed. These are both great sources of microbial innoculation to help the seeds get the best possible germination rate, and because we had access to both we gave it a double whammy!

The green manure seed mix, mixed with worm castings and soaked in whey
The green manure seed mix, mixed with worm castings and soaked in whey

This left the seed mix pretty wet, so then we mixed it with enough dry sand to make it spreadable.

The reason we were inspired to increase the diversity of our green manure seed mix was that Dr Jones explained that prior to European invasion, “the natural grasslands that once covered vast tracts of the Australian, North American, South American and sub-Saharan African continents – plus the ‘meadows’ of Europe – contained several hundred different kinds of grasses and forbs.”

Several hundred species! Imagine that!

A multi-species crop is an entire community of plants working together to convert sunlight into liquid carbon (remember learning about photosynthesis at school?) which it feeds the microbes in the soil. It’s called the plant-microbe bridge, and it builds soil, converts carbon from the air into stable compounds in the soil and holds far more water in the soil.

So, feeling inspired, we set out to create our own multi-species crop. We didn’t quite get to 100 species, but we managed 40:

  • Alfalfa (lucerne)
  • Amaranth
  • Basil
  • Beetroot
  • Broad bean
  • Buckwheat
  • Butterfly pea
  • Chia
  • Cocksfoot
  • Coriander
  • Corn
  • Dill
  • Endive
  • Fenugreek
  • Kidney beans
  • Lab lab bean
  • Linseed
  • Medic
  • Millet – French white
  • Mung bean
  • Mustard
  • Purslane
  • Quinoa
  • Radish
  • Rocket
  • Sesame
  • Soy bean
  • Sunflower
  • Turnip
  • Vetch

Now we just have to get them to grow! Stay tuned for photos….and if you’d like to find out more about how to quickly build fertile soil at your place using green manures, we’ve packed a lot more detail into this short course.