Improve Fruit Set and Quality with Calcium and Boron: A Guide

Why fruit set and quality depend on calcium and boron

Many growers see plenty of flowers but too few fruits, or fruits that drop, crack or rot at the tip before harvest. Very often the cause is not a lack of NPK but a shortage of two nutrients needed in small amounts at exactly the right time: calcium and boron.

Both move poorly inside the plant. Calcium travels mainly with the water stream to leaves, so fast-growing fruits often get less than they need. Boron is not easily moved from old leaves to new growth. This means a plant can look healthy while its flowers and fruits are short of these nutrients.

What calcium and boron do

Together, they support flowering, pollination, fruit set, fruit firmness and shelf life.

Deficiency symptoms to watch for

Symptoms show first on new growth, flowers and fruits, because neither nutrient moves easily from older tissue.

Calcium deficiency:

• Blossom-end rot – a dark, sunken patch at the bottom of the fruit, common in tomato, chilli and capsicum.
• Fruit cracking and poor firmness.
• Tip burn or distorted young leaves.
• Poor keeping quality after harvest.

Boron deficiency:

• Heavy flower and young fruit drop.
• Poor fruit set even with good flowering.
• Misshapen, cracked or corky fruits.
• Hollow stems or internal browning in some vegetables.
• Death of growing tips and brittle young leaves.

Fruit cracking and fruit drop can have several causes, including irregular watering, heat and pests. Check irrigation and crop protection along with nutrition.

Step-by-step: a calcium and boron programme

Step 1: Fix the basics first

1. Test soil pH and nutrient status. Boron availability is often low in sandy, high-pH and low-organic-matter soils.
2. Keep irrigation steady. Long dry spells followed by heavy watering are a leading trigger for blossom-end rot and fruit cracking.
3. Avoid excess nitrogen and potash, which can compete with calcium uptake.
4. Mulch where possible to keep soil moisture even.

Step 2: Spray at the right stages

Foliar sprays work best when timed to the crop's demand. A practical timing plan:

The number of sprays and the interval depend on the crop and its flowering pattern. Crops that flower and fruit over a long period, such as tomato and chilli, usually need repeat applications.

Step 3: Use CaB Plus for calcium and boron together

CaB Plus is a certified organic nutritional supplement with naturally chelated calcium and boron. It has 20% organic content, higher antioxidant activity and natural surfactants for better nutrient penetration.

• Dose: 400 ml per acre, or 2.5–3 ml per litre of water.

Benefits:

• Corrects calcium and boron deficiencies immediately.
• Reduced dropping of fruits and vegetables.
• Enhanced fruit setting.
• Reduced blossom-end rot in vegetables.
• Better quality of fruits and vegetables.
• Better post-harvest quality – size, colour and turgidity – and increased shelf life.

Step 4: Add Calci-Phite where calcium demand is high

Calci-Phite™ is a concentrated nutrient solution containing highly soluble calcium, potash and phosphites. It accelerates nutrient acquisition and assimilation and supports growth, flowering, fruit set, rooting and transplant establishment, while strengthening the plant's immune system.

• Dose: 300–400 ml per acre.
• Crops: all crops.
• Compatibility: most common pesticides, chemically neutral fertilizers and micronutrients.

Step 5: Support flowering with primacyALPHA

primacyALPHA® works inside the plant to stimulate efficient assimilation and utilisation of nutrients. It is a blend of a cytokinin precursor, a chlorophyll precursor and Take Off technology, and acts as a reproductive growth catalyst. It increases flowering, fruit size and fruit set, and provides critical secondary and micronutrients including sulphur, boron, manganese and zinc.

• Dose: 400 ml per acre, or 2.5–3 ml per litre of water.

Step 6: Finish with Cyto Potash at colour change

Cyto Potash is an organic liquid potash (14%) with natural ligands for easy application and rapid absorption. In fruits and vegetables, it is applied at the colour-change stage to support fruit size, weight and colour formation. It also acts as an osmoregulator, improving tolerance to abiotic stress, especially drought.

• Dose: 250 ml per acre, or 1.5–2 ml per litre of water.

Spraying tips

• Spray in the cool part of the day – early morning or late evening.
• Cover both sides of leaves and the developing fruit clusters.
• Use clean water and the correct dose; more is not better.
• Do a small jar test before tank-mixing any two products for the first time, and follow each label.
• Avoid spraying just before rain.

Common mistakes to avoid

• Spraying only after symptoms appear. Blossom-end rot and cracking cannot be reversed on affected fruit. Start before flowering.
• One spray for the whole season. Calcium and boron move poorly in the plant, so repeated applications through flowering and fruiting work better.
• Ignoring irrigation. Irregular watering causes blossom-end rot and cracking even when calcium is applied.
• Overdosing boron. The gap between enough and too much boron is narrow. Stick to label doses.
• Mixing without checking. Some calcium products react with phosphates or sulphates. Check labels and jar test.
• Too much nitrogen at flowering. It pushes leafy growth at the cost of fruit set.

Quick checklist

• Soil tested; irrigation kept steady
• Pre-flowering spray planned
• Spray at fruit set to reduce flower and fruit drop
• Repeat sprays during fruit development
• Cyto Potash at colour change
• Doses measured as per label; sprays in cool hours

Talk to a Verdesian agronomist

The right calcium-boron programme depends on your crop, soil and flowering pattern. Contact a Verdesian agronomist for a crop-specific spray schedule, or request trial reports to see results in your crop.

Frequently asked questions