The olive tree only unfolds its Mediterranean flair with the right care. We show how, when and with what to properly fertilise your olive tree.
Olive trees (Olea europaea) originally grow in the Mediterranean region on poor, nutrient-poor and stony soils. They are very hardy and quite undemanding. Due to the climate, most olive trees in our latitudes are cultivated in pots. Here, the soil volume and consequently the nutrient supply is severely limited, and regular fertilisation becomes necessary even for slow-growing woody plants. When feeding olive trees, you should take into account the individual nutrient requirements of the Mediterranean plant: Season, age of the olive tree and location determine the need for nitrogen, potassium, etc. An adapted fertiliser application at the right time is therefore essential for healthy growth and resistant plants.
When to fertilise olive trees?
Fertilise olive trees only in the growth phase between April and September. When overwintering the olive tree during the cold season, fertilisation should be stopped altogether. Olive trees should be repotted every few years and moved to fresh, nutrient-rich potting soil. No fertilisation is necessary for the first few months after re-potting the olive tree, unless deficiency symptoms appear. If an olive tree does not show any symptoms of deficiency and has a healthy growth, it usually does not need fertilising.
Young olive trees up to two years of age should be fertilised at a very reduced rate, if at all. For them, a quarter to a third of the recommended amount of fertiliser is enough. Seedlings and cuttings are not fed at all.
Tip: For planted out saplings, you can provide increased winter hardiness by autumn fertilising with potassium fertiliser. The potassium helps harden the shoots and makes them less sensitive to frost.
At a glance: When should you fertilise an olive tree?
- Olive trees in pots are fertilised during the growth phase between April and the end of September.
- Freshly repotted olive trees do not require any fertilisation for the first few months.
- Planted olive trees usually do not need plant food, but autumn fertilisation with potassium fertiliser increases winter hardiness.
- During winter dormancy, the olive tree is not fertilised.
Recognising deficiency symptoms
- Nitrogen deficiency: Even the frugal olives can develop a nutrient deficit. Most often, this is a nitrogen deficiency. This is noticeable by a yellowing of the leaves and very restricted growth. If this has not been repotted or fed for some time, a nitrogen deficiency is likely.
Note: Excessive water and waterlogging at the roots can also trigger these symptoms. So before reaching for fertiliser, check whether the water has been standing in the container for days or whether the soil has been wet for a long time.
- Potassium deficiency: Potassium deficiency causes withering of leaf tips to death of entire shoots.
- Calcium deficiency: Olives prefer a slightly alkaline soil with a pH of 7 – 8. If the pH is too low, calcium deficiency may occur. This manifests itself in a yellowing of the leaves from the tip. Increasingly, the entire leaf discolours and the veins also lighten. Calcium-containing lime increases the pH value and at the same time provides the missing nutrient. However, first check the pH of the soil.
- Phosphorus deficiency: A pronounced phosphorus deficiency in olives and manifests as a reddish colouration of the leaves, but is exceedingly rare.
Olive tree fertiliser: what to use and how much?
Special fertilisers for olive and lemon trees etc. have an optimal composition of nutrients for Mediterranean plants. They are usually commercially available under the name of citrus fertiliser. If you do not want to buy a special olive tree fertiliser, use a balanced NK fertiliser. Phosphorus is needed for flowering and fruiting, but is usually present in sufficient quantities in high-quality potting soils. Preferably, the plant food used should also contain other nutrients in traces, such as boron, iron, manganese, molybdenum and zinc. In high-quality potting soil, these trace elements are also usually present in sufficient quantities until the next repotting.
It should also be noted that an olive tree that receives a lot of light and heat, grows faster than in unfavourable locations. It therefore consumes more nutrients here, which are reflected in higher fertiliser requirements. The type of fertiliser is also critical to the frequency of fertilisation.
Summary: With what and how much should you feed an olive tree?
- Special citrus fertilisers are suitable in composition for olives and most other Mediterranean plants.
- Alternatively, universal fertilisers emphasizing nitrogen (N) and potassium (K), ideally with other micronutrients, can be used.
- Fertilisation depends on age, location and type of fertiliser.
Feeding olive trees with liquid plant food
Especially for the frugal Mediterranean trees, a natural nutrient supply is beneficial. Here, the nutrients are stored in the soil and gradually made available to the roots. Fertilisers with a high content of organic matter, such as compost or easy-to-apply liquid fertilisers, such as our Plantura Liquid Citrus Food, therefore have a gentle mode method of action. It is not just the soil life that benefits from the application of these fertilisers. There is also little risk of overfertilisation. By using vegetable residues from the food industry, the environment and valuable resources are conserved. Olives are fertilised with our liquid fertiliser about every two weeks through the irrigation water. To do this, mix 15 – 25 ml of the fertiliser to 5 litres of water and then water the olive tree as needed.
Feeding olive trees with mineral fertiliser
If the olive tree suffers from a severe nitrogen deficiency, mineral fertilisers can quickly remedy the situation. This can be recognised, among other things, by stunted growth or leaf drop after chlorosis. The nutrients are water-solubly bound in mineral fertilisers and contained in a form directly available to the plant. However, in the long term, the administration of mineral plant food is not recommended. Especially with frugal plants like the olive tree, the risk of overfertilisation is high and the sensitive plant roots can be damaged. Heavy watering or rain additionally pose the risk of washing out the water-soluble fertilisers. Furthermore, mineral fertilisers are mostly associated with high energy consumption and costs for the environment.
Feeding olive trees with home remedies
Coffee grounds are a daily waste product in many households, but still have a high nitrogen content. In small dosage and superficially incorporated, this is slowly released. However, if you would like to fertilise your olive tree with coffee grounds, you should keep in mind that as they decompose, they lower the pH value of the soil. Remedy for soil acidification is fertilisation with crushed eggshells, which increase soil pH.
More unusual plant food such as nails and hair, by the way, can be used in the garden as a substitute for bone meal.
Home remedies also include plant extracts such as stinging nettle liquid fertiliser. In addition to numerous micronutrients, fermented broths often possess not insignificant amounts of nitrogen and can even be used undiluted against pests such as leaf aphids (Aphioideae). In addition, for planted specimens, a slurry of comfrey (Sympthytum officinale) in the autumn can serve as a potassium source to increase winter hardiness.
Feeding olive trees: recognising overfertilisation
Overfertilisation poses the much higher risk compared to deficiency. Overfertilisation often manifests itself in the form of burning symptoms called nutrient burn. Shortly after fertilisation, the leaves get yellow-brown tips and edges, which increasingly move inward and because the whole leaf to dry up. The leaves can also curl up in places. Affected leaves usually fall off promptly. With only a slight overfertilisation with nitrogen, the olive tree develops long, thin shoots and hardly forms flowers, but mainly leaves. Remedy for acute overfertilisation – for example, by fast-acting mineral fertilisers – is repotting in fresh planting soil. As much as possible of the overfertilised soil should be removed from the root ball or rinsed off.
Another important care measure for olive trees is proper pruning. How and when to prune olive trees is explained in our special article.