Autumn fertilization of orchards, vineyards and olive groves: guide

In short. Autumn fertilization is carried out after harvesting, before the leaves fall and the soil cools down. It serves to replenish the plant’s reserves for vegetative growth and to return organic matter to the soil. In our experience, it is advisable to prioritize phosphorus, potassium, and slow-release organic fertilizers, while limiting readily available nitrogen.

Every year, when the harvest ends, many agricultural companies consider the season over. We see it differently: for the arboreal crops, autumn is the time when much of the subsequent production is prepared. Flowering, fruiting, and vigor of budding depend largely on the reserves that the plant manages to accumulate in the months following harvest.

In this article we share how we set up autumn fertilization together with the fruit, wine and olive oil companies we follow: when to intervene, what elements to add and which formulations to choose.

Why we fertilize in autumn: the plant's reserves

After harvesting, the arboreal plants do not immediately enter a dormant state. As long as the leaves remain functional and the soil is still warm, the roots and crown continue to work: they absorb nutrients and store them in the form of starch and nitrogenous compounds in the roots, trunk, and branches.

It is precisely these reserves that fuel the spring revival, when the plant sprouts and flowers before it has a leaf system capable of supporting it. Therefore, when an autumn fertilization is well calibrated, we observe in the field:

• more uniform and vigorous sprouting;
• better differentiation and quality of flower-shaped gems;
• a greater tolerance to early-season stresses, such as late frosts and temperature fluctuations;
• the recovery of the fertility of a soil depleted by the production of the previous year.

When to apply autumn fertilization

The useful window extends from the collection to the fall of the leaves. Roughly speaking, we are talking about the period between September and November in the Central and Southern regions, with a few weeks of advance in the North. These are the timing recommendations for the main crops:

It should be remembered that in Nitrate Vulnerable Zones there are seasonal distribution bans for certain categories of fertilizers. Before planning interventions, it is always necessary to check the schedule provided by the action program of your region.

What elements to add in autumn

Phosphorus. It supports radical development and the formation of buds. Since it is poorly mobile in the soil, we always distribute it in a localized manner, close to the active root system.

Potassium. It improves tissue lignification, cold resistance and the quality of future productions.

Nitrogen. In autumn we use it with caution. We prefer slow-release organic nitrogen: readily available mineral nitrogen risks stimulating late-season vegetation that is sensitive to cold or being washed away by winter rains.

Magnesium and sulfur. Magnesium is essential for chlorophyll, and sulfur is essential for protein synthesis. In depleted soils, it is often found in short supply.

Organic substance. It is the element that, in our opinion, distinguishes professional autumn fertilization. Organic carbon and humic and fulvic fractions improve soil structure, water retention and capacity to exchange nutrients, and nourish beneficial microflora.

Organic, organo-mineral or mineral: what do we choose

In autumn, for arboreal crops, our choice almost always falls on an organo-mineral or organic fertilizer. These formulations release the nutrients gradually, in tune with the slower absorption rhythms of the season, while at the same time providing organic matter.

We developed the Dualtech line based on this principle: organic matrices enriched with a selected microflora to make the best use of the residual fertility of the soil.

Dualtech N 12 Bio We recommend it in soils with a good supply of phosphorus and potassium, where nitrogen and organic matter are especially needed.

NPK 4-3-3 Bio It is our granular organic fertilizer obtained from cattle and equine manure, dried pollina and borlanda, with the Micro Active Complex technology. We recommend it when the priority is to reconstitute the organic matter.

The role of microorganisms and mycorrhizae

Providing nutrients is not enough if the soil is unable to make them available. In autumn, with temperatures still mild and rainfall keeping the soil moist, the beneficial microorganisms find ideal conditions to settle in the rhizosphere.

For this reason, we often combine organic fertilization with an inoculation of mycorrhizal fungi such as Fungy Star. In this way we help the plant to:

• to extend the surface area of soil explored by the roots;
• better absorb phosphorus and microelements;
• recovering biological fertility in the most exploited soils.

Those who want to learn more can read our guide on soil micro-organisms and the article about’regenerative agriculture.

How to set up an autumn fertilization plan in 5 steps

1. Let’s start with the analysis of the soil: phosphorus, potassium, magnesium, organic matter, pH and active limestone. Without analysis, the risk of overdosing or under-dosing is high.
2. We estimate removals, that is, how much the production of the year subtracted from the land based on the yield.
3. We choose the formulation: an organo-mineral with predominant phosphorus and potassium and organic nitrogen, or a pure organic formulation if the organic matter is low.
4. We distribute it in a localized way along the row or in the projection area of the canopy, where the roots are active, with a slight planting when possible.
5. We integrate it with a mycorrhizal inoculant or a microbial consortium to increase the efficiency of nutrient use.

The errors we see most often

• Fertilize with fallen leaves and cold soil: absorption is minimal and losses increase.
• Using nitric oxide in autumn: it stimulates late frosts and is easily washed away.
• Distribute the phosphorus over a wide area, where it will be immobilized away from the roots.
• Focusing solely on the mineral elements while neglecting the organic substance.

Let's build your plan together

Each company has different land, crops and objectives. Our technicians are available to build a customized autumn fertilization plan based on the soil analysis. Contact us or register to download the technical sheets of our products.

Frequently asked questions about autumn fertilization

When is autumn fertilization done?

In the post-harvest period, before the leaves fall and the soil cools down. In Italy, the window typically runs from September to November, with an earlier start in the North and a later start for the olive trees in the Central and Southern regions.

Which fertilizer should be used in autumn for fruit trees?

We recommend an organo-mineral fertilizer with phosphorus and potassium predominating over nitrogen, preferably with slow-release organic nitrogen and humic carbon. An example is our product FUNGY STAR, Allowed in organic agriculture.

Can nitrogen be applied in autumn?

Yes, but in limited quantities and in an organic form. The readily available mineral nitrogen can stimulate late-season vegetation sensitive to frost and be washed away by the winter rains.

How much organo-mineral fertilizer is needed per hectare in a fruit orchard or vineyard?

For drupes, olives and vines we indicate by Dualtech N 12 300-700 kg/ha in localized distribution. The exact dose depends on soil analysis, plant age, and yield.

When to fertilize the olive tree in autumn?

After the olive harvest and before the cold weather, usually between November and December in the Central-South region. The goal is to replenish reserves for vegetative growth and production capacity.

Can mycorrhizae be applied in autumn?

Yes. With the soil still warm and moist, the conditions are favorable for the colonization of the roots. Distributing the inoculum along with the organic fertilizer improves its effectiveness.