Organic Fertilization of Fruit Trees

In order to develop and produce, fruit trees draw on the soil’s reserves and consequently impoverish them.

Organic Fertilization of Fruit Trees
Compost and bark mulch at the base of a persimmon tree

Unlike conventional nursery stock, which aims to feed the fruit tree directly and thereby inexorably deplete the soil, the biological fertilization of fruit trees (or rather of the orchard) will consist in maintaining, or even improving, the organic matter (and therefore nutrients) content of the soil in a balanced way.

But first, let’s see what these essential nutrients are for fertilizing fruit trees (or an orchard).

Nutritional Needs of Fruit Trees

Nutrients are multiple and complementary:

  • Nitrogen : nitrogen is the basic element for the formation of the green parts of the plant (twigs and leaves) but also the buds and flower buds. Nitrogen is also essential for fruit size.
  • Phosphorus : Phosphorus plays a major role in the fruiting (fruit setting) process. It is also important for proper ripeness and for the flavor of the fruit.
  • potash : potash allows the hardening of the branches and the formation of flowers. The sugar content of the fruit also depends on the potash.
  • Calcium : due to its effect on the physical life of the soil, calcium is also an important element for the balance of an orchard.
  • Secondary Elements : sulfur, magnesium, sodium. Although they play a minor role, these elements are essential for the proper balance of the orchard.
  • trace elements : iron, copper, zinc, boron, manganese, molybdenum, chlorine, cobaltā€¦ in fact the trees trap a large part of these elements in the air. However, their presence in the ground is also fundamental. They are only absorbed by plants due to the presence of organic matter in the soil.

So we can see that to be healthy and productive, an orchard needs all these nutrients.

But how do you know if this or that element is missing?

Identify and fix an orchard’s shortcomings

First of all, keep in mind that regular additions of compost are generally sufficient to limit deficiencies.

However, if you want to know the richness of a soil before planting fruit trees, you can of course perform a full physical and chemical analysis of the soil (including trace elements).

Then theobservation also helps to identify any shortcomings:

  • Low-nitrogen soil : the growth of the tree will be very weak, even stopped. The leaves are small and you can see orange spots along their midribs. Young twigs can dry out. Large and regular additions of compost will generally suffice to make up for these deficiencies. You can also water at the base with nettle fertilizer or comfrey fertilizer diluted to 10%.
  • Soil with a lack of phosphorus : The undersides of the leaves have a purple vein, the leaves are small and dull and the buds tend to dry out. Phosphorus deficiency is relatively rare. Again, regular addition of compost is generally sufficient to prevent a phosphorus deficiency. A few sprinklings of comfrey (diluted to 10%) will also be beneficial. If necessary, we can make an extra contribution of bone meal.
  • Soil low in potassium : the leaves curl up and the edges are dark brown (especially noticeable in apple trees). The fruits do not keep well. Regular fertilization with compost prevents this kind of deficiency. However, sometimes it can be useful to add potassium in organic form: wood ash, beet vinasseā€¦ Comfrey manure also works wonders here.
  • Soil low in calcium : the fruits remain green. Calcium deficiencies are observed in acidic soil or after an excessive supply of poorly decomposed organic matter (preferably use mature compost) which will block assimilation by the plant. A fertilizer made from seaweed can be useful in acidic soil.
  • Low-sulphur soil : very rare and difficult to observe phenomenon.
  • Low in magnesium : Due to an excess of potassium or a lack of organic matter, magnesium deficiencies are common in apple trees, pear trees, peach trees or cherry trees.
  • Soil with a deficiency of trace elements : we will not go into detail on the possible shortcomings of the various trace elements. Just know that the compost, by allowing the trace elements present in the soil to be absorbed by the plant, also plays a major role in this. Today, there are natural solutions rich in trace elements on the market.

As we have just seen, compost will be the most important part of the organic fertilization of fruit trees. We will now see in more detail how to carry out this fertilization.

Basal fertilization of fruit trees (at planting)

At the beginning of their life, fruit trees have a particularly high nitrogen requirement (an element necessary for their growth).

  • Put compost (well digested) at the bottom of the planting hole
  • When planting, cover the roots with deep soil mixed with compost
  • Fill with topsoil also mixed with compost
  • If the soil is low in nitrogen, this basic fertilizer can be supplemented with an organic nitrogen fertilizer (e.g. castor cake)

Maintenance fertilizer – what to put under fruit trees?

At full production, the nitrogen requirements of fruit trees decrease, even if they remain high (the roots of fruit trees can then pull this element deeper); in contrast to the needs for potassium and phosphorus (important elements for flowering and fruiting) which become more consistent.

  • Every 2 to 5 years, depending on the soil richness, in the autumn bring compost (digested or not) or manure (even slightly digested) in sufficient quantity (one wheelbarrow per tree is perfect) at the base of the tree (weeds first) weeding). The earthworms ensure a gradual burial and thus promote soil life.
  • In a phosphorus-poor soil, the manure can be supplemented with an organic fertilizer rich in phosphorus (bone meal) at the same time as the addition of compost.
  • In the spring, in potash-poor soil, apply an organic fertilizer rich in potassium (e.g. comfrey or beetroot vinasse)

Avoid adding compost every year, this would lead to shallow rooting, the tree will then be content with the fertilizer available at the surface. For good rooting, it is best to let the tree root deeply.

This maintenance fertilization will be all the more effective if some complementary techniques are also applied.

The front orchard

Instead of cultivating the orchard’s soil, we preferred to cover the orchard’s soil with spontaneous vegetation, or to create a culture of green manures (the ideal is a mixture of, in particular, some spring flowers that pollinate your fruit trees well).

These techniques have the advantage that they limit erosion, increase the humus content of the soil and thus increase the absorbability of the trace elements present in the soil.

Mulching (or permanent mulching)

Mulching consists of permanently covering the ground with straw or other plant debris (especially grasses mowed from the front orchard, etc.)

After adding compost, lay the mulch in a layer 15 to 20 cm below the crown of the tree.

As it decomposes, the mulch will complete the compost supply while protecting it.

Mulching also has the advantage of maintaining a certain coolness at the base of the tree or dampening the fall of fruit.

A good mulch gradually turns into rich humus. Good that you say! Yes, of course, but this mulch, by becoming food for the tree, will also have the effect of attracting the roots of young trees superficially (and thus making them more vulnerable)… To prevent this, and on the contrary allow to root in the depth, during the first years of the tree’s growth, it is preferable to use covering materials that release few mineral elements (for example, rough straw).

Beware of rodents!

Purins and other herbal preparations

As we have seen above, preparations based on nettle (see here) or comfrey root (see here) will also have a beneficial effect on fruit crops, especially due to the trace elements they contain.

However, keep in mind that these are fertilizer supplements. Like chemical fertilizers, they feed the plant directly (in this case fruit trees), but in no way can they replace the organic fertilizer (which will feed the soil … soil which will then be able to bring all the elements necessary are for growth but also for good fruiting of your fruit trees).

When watering fruit trees (at least free trees) that sometimes require professional equipment, the amateur gardener will find it easier to use slurry when watering at the base of the tree. The manure must first be diluted to 10%.

  • Do you think your fruit trees are deficient, but can’t determine where the problem is coming from?
  • Are you unsure about fertilizing your fruit trees?
  • Are pests or diseases destroying your crops?

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