📊 2026 Olive Feeding Calendar
Northern Hemisphere: March–April: High-N (21-0-0). May: Foliar Boron at 5–10% bloom. July: Balanced NPK (10-10-10). August–September: High-K (0-0-50, Potassium Sulfate only). Southern Hemisphere: September–October: High-N. November: Foliar Boron. January: Balanced NPK. February–March: High-K before harvest.
The Boron Secret: Why Most Olive Groves Fail at Fruit Set
Boron (B) is the single most limiting micronutrient in commercial olive production, a fact reinforced by the UC Davis Olive Center research on nutrient management which confirms that deficiency can cause 40% fruit drop
The Pollen Failure Mechanism
Boron is essential for pollen tube germination during the inflorescence stage. Without adequate B levels (>25 ppm in leaf tissue), pollen grains fail to reach the ovary. The result: blank drupes that abort within 3–4 weeks of flowering.
Visual Symptoms
- “Witch’s Broom” growth: Dense clusters of stunted shoots at branch tips.
- Premature fruit drop before pit hardening (mid-June in Northern Hemisphere).
- Corky bark lesions on 2-year wood.
Application Protocol
Apply Solubor (20.5% B) or Borax (11% B) as a foliar spray at 5–10% bloom. Target rate: 0.5–1.0 lb Boron per acre. Split into two applications 10 days apart to avoid phytotoxicity. Never exceed 2 lb B/acre per season.
Caution: Boron is a heavy metal. Symptoms of toxicity (leaf tip burn) appear at >150 ppm. Never ‘eye-ball’ Boron measurements; use a digital scale.
[Insert image: Close-up of olive flowers with pollen tubes under microscope]
Managing “Alternate Bearing”: The Nitrogen Strategy
Alternate bearing is the industry’s $200 million problem. Olive trees evolved to conserve energy by alternating heavy crop years (“On-Years”) with light years (“Off-Years”). Modern nutrition can break this cycle.
The Fruiting Wood Principle
Olives fruit on one-year-old wood. The shoots grown in 2025 bear fruit in 2026. During an On-Year with heavy fruit load, trees often fail to produce sufficient vegetative growth for next season’s crop.
Early-Season Nitrogen Intervention
Apply high-N fertilizers (21-0-0 Ammonium Sulfate or 46-0-0 Urea) in late winter (February–March in Northern Hemisphere). Target rate: 100–150 lb N/acre for mature orchards.
This timing stimulates shoot elongation before the tree commits energy to fruit development. The result: adequate fruiting wood formation even during heavy crop years.
Critical Cutoff Date
Cease all Nitrogen applications by mid-August. Late-season N promotes soft, frost-sensitive growth that cannot complete hardening off before winter. Late-season nitrogen creates soft growth that is highly susceptible to frost; current University of Florida IFAS Extension guidelines show that cold damage is 60% higher in groves fertilized after mid-August.
The Oil Synthesis Phase: Potassium’s Role in Drupe Quality
Olive oil accumulation occurs during the final 60–90 days before harvest. Potassium (K) is the rate-limiting nutrient during this critical window.
Biochemical Function
K regulates osmotic pressure in drupe cells, enabling lipid synthesis and transport. It also activates over 60 enzymes involved in fatty acid metabolism. Trees deficient in K produce oil with lower oleic acid content and reduced shelf stability.
The Chloride Problem
Never use Muriate of Potash (KCl) on olives. Olea europaea is extremely sensitive to chloride toxicity. Symptoms appear at >0.25% Cl in leaf tissue: marginal leaf burn, premature defoliation, and reduced oil percentage.
Potassium Sulfate Protocol
Apply Potassium Sulfate (K₂SO₄, 0-0-50) in late summer (August–September in Northern Hemisphere). Split application: 150 lb/acre at color break (drupes turn from green to purple), followed by 100 lb/acre 3–4 weeks later.
The sulfate form provides dual benefits: K for oil synthesis and sulfur (S) for amino acid production. Target leaf tissue levels: 1.2–1.8% K.
Oil Quality Impact
UC Davis trials demonstrate 12–18% higher oil content in drupes with optimized K nutrition. More critically, K-sufficient trees produce oil with 15% lower peroxide values (PV) after 12 months storage—a key marker of oxidative stability.
Olive Fertilizer Matrix 2026
| Fertilizer Type | Key Nutrient | Timing | Economic Impact on Yield |
|---|---|---|---|
| Ammonium Sulfate (21-0-0) | Nitrogen (N) | Late Winter (Feb–Mar) | +20% shoot growth; breaks alternate bearing |
| Solubor Foliar Spray | Boron (B) | 5–10% Bloom (May) | +30% fruit set; prevents pollen failure |
| Balanced NPK (10-10-10) | N-P-K | Fruit Set (July) | +12% overall yield; supports pit hardening |
| Potassium Sulfate (0-0-50) | Potassium (K) | Late Summer (Aug–Sep) | +15% oil content; improves shelf life |
| Calcium Nitrate (15.5-0-0) | Nitrogen + Calcium | Early Spring (March) | Ideal for calcareous soils; no pH change |
Soil pH and Drainage: The Foundation Requirements
Olives are calcicoles—plants that thrive in alkaline, calcium-rich soils. Optimal pH range: 6.5–8.5.
While olives prefer alkaline conditions, maintaining precise levels is key. If your soil is too acidic, follow our guide on how to manage soil pH for technical adjustment steps.
Calcareous Soil Tolerance
Unlike most fruit crops, olives tolerate high calcium carbonate levels (up to 40% CaCO₃). They’ve evolved chelation mechanisms to access iron (Fe) and zinc (Zn) in alkaline conditions.
The Drainage Critical Point
Poor drainage is lethal. Olives require 60–90 cm of well-aerated soil. Waterlogged roots develop Phytophthora root rot within 48–72 hours. If your site has clay hardpan or standing water, install subsurface drainage tiles before planting.
Common Fertilizer Mistakes to Avoid
1. Using Citrus Fertilizers
Citrus blends are high in nitrogen and low in potassium—the opposite of olive requirements during oil accumulation. They also contain chloride-based K sources.
2. Late-Season Nitrogen
Applying N after mid-August causes soft growth that freezes at -5°C instead of the -12°C tolerance of hardened wood.
Excessive late-season nitrogen is a common error; learn how to identify over-fertilization versus nitrogen deficiency symptoms in our technical guide.
3. Ignoring Micronutrients
While N-P-K dominates discussion, Boron, Zinc, and Manganese deficiencies cause silent 20–30% yield losses. Annual soil and leaf tissue testing is mandatory.
4. Overfertilization
More is not better. Excessive N (>200 lb/acre) promotes vegetative growth at the expense of fruiting and increases Verticillium wilt susceptibility.
Leaf Tissue Analysis: The Diagnostic Standard
Visual symptoms appear 4–6 weeks after nutrient deficiency begins. Leaf tissue analysis provides early warning.
Sample Collection Protocol
- Collect 100 leaves from current-season growth in mid-July.
- Select leaves from mid-shoot position (avoid terminals and basal leaves).
- Send to a certified lab for complete nutrient profile.
Critical Threshold Values
- Nitrogen: 1.4–1.8%
- Phosphorus: 0.1–0.3%
- Potassium: 1.0–2.0%
- Boron: 19–150 ppm
- Chloride: <0.25% (toxicity above this level)
FAQ Schema: Technical Olive Nutrition
Q: Can I use citrus fertilizer for olives?
No. Citrus formulations are N-heavy (2-1-1 or 3-1-1 ratios) and often contain chloride-based potassium. Olives require K-heavy nutrition (1-1-2 ratios) during oil synthesis and are extremely sensitive to chloride toxicity.
Q: When is it too late to fertilize olives?
Cease nitrogen applications by mid-August in temperate zones. Late N promotes frost-sensitive growth. Final potassium applications should occur 4–6 weeks before harvest to allow nutrient translocation into drupes.
Q: Why are my olive leaves yellow with green tips?
This “interveinal chlorosis” pattern indicates potassium deficiency (if older leaves are affected) or boron deficiency (if new growth shows symptoms plus tip dieback). Yellow leaves with green veins suggest iron deficiency in excessively alkaline soils (pH >8.5).