Best Fertilizer for Begonias: Feeding Tips for Healthy Blooms and Foliage

Understanding Begonia Varieties and Their Nutritional Needs

Begonias are a diverse and vibrant genus of flowering plants prized for their colourful blossoms and patterned foliage. Whether you’re growing tuberous begonias in hanging baskets, wax begonias in bedding displays, or rhizomatous types as indoor ornamentals, all begonias share a need for consistent but balanced nutrition. Knowing when and how to feed them is essential for lush foliage and continuous blooming.

Most begonias thrive in part-shade, preferring filtered light and rich, well-draining soil. Their delicate roots are susceptible to rot, so overwatering and over-fertilising are common causes of failure. However, with the right fertiliser, your begonias will thrive through their active growth season, typically from early spring through late summer in most parts of Australia.

The best fertilizer for begonias early in the season is one that encourages foliage development and root health without overloading nitrogen. A balanced fertiliser such as the CompleteGrow 20-20-20 Powder Fertiliser provides equal ratios of nitrogen (N), phosphorus (P), and potassium (K), plus essential micronutrients to support compact growth and bud initiation.

Start feeding your begonias once new growth emerges, usually 2–3 weeks after planting. Use 1 gram of fertiliser per litre of water and apply every 10–14 days. This supports strong root development and foliage expansion, setting the stage for vibrant blooming later in the cycle. Avoid granular fertilisers for begonias, as they can cause root damage and uneven nutrient uptake.

If you’re growing tuberous begonias in pots or baskets, be especially mindful of watering. Allow the soil to dry slightly between waterings to avoid fungal problems. Feeding during the early stages helps maximise tuber energy use, allowing for larger blooms later in the season.

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Feeding for Flower Power: Boosting Blooms in Mid to Late Season

As begonias shift into their blooming phase, typically 6–8 weeks after active growth begins, their fertiliser needs change. The best fertilizer for begonias during flowering contains reduced nitrogen and increased phosphorus and potassium to support bud development, vibrant colour, and longer-lasting flowers.

This is particularly important for tuberous begonias, which are prized for their showy, oversized flowers in hanging baskets and patio pots. A bloom-focused fertiliser like the CompleteGrow 4-18-38 + CaMg Fertiliser offers the ideal ratio for this stage: low nitrogen (4%) to prevent excessive leafy growth, high phosphorus (18%) for blooming, and potassium (38%) to intensify colour, strengthen stems, and extend flowering.

Apply this fertiliser every 7–10 days during peak bloom time, starting when you see buds forming. For hanging basket begonias or potted wax begonias, continue the same dilution (1g per litre) and apply early in the day to avoid nutrient burn. The inclusion of calcium and magnesium is especially important, helping prevent tip burn, weak stems, and leaf discolouration.

Monitor your begonias closely for signs of nutrient stress. Yellowing between veins can indicate magnesium deficiency, while pale flowers or leaf drop may be due to potassium or calcium shortages. Regular feeding with a complete product like 4-18-38 ensures your begonias receive everything they need to keep flowering continuously through summer.

In cooler areas like Tasmania or Victoria, begonias will begin slowing growth as temperatures drop. Cut back feeding in early autumn and cease altogether once plants begin entering dormancy, especially for tuberous types.

Container Fertilising Tips, Begonia Issues & FAQs

Begonias grown in containers, whether decorative pots or hanging baskets, require more frequent feeding than those in garden beds. Nutrients quickly wash out of potting mixes, especially during summer rains or frequent watering. To maintain lush growth and continuous flowering, the best fertilizer for begonias in pots is a fast-acting, water-soluble formula applied on a regular schedule.

Alternate between a balanced fertiliser (20-20-20) and a bloom booster (4-18-38) every week for best results. Apply only to moist soil and avoid wetting the foliage to prevent fungal leaf spots. Always use a well-draining potting mix, and repot annually with fresh soil to avoid salt build-up and nutrient imbalance.

If your begonias stop blooming or appear leggy, check for root crowding, insufficient light, or overfeeding with nitrogen. Tuberous begonias may also enter dormancy early if stressed by heat, poor nutrition, or pests such as aphids or thrips.

FAQs: Best Fertiliser for Begonias

Q: What is the best fertilizer for begonias in hanging baskets?
Use a water-soluble fertiliser like CompleteGrow 20-20-20 early on, then switch to 4-18-38 + CaMg to support flowering and strong stems.

Q: How often should I fertilise begonias in pots?
Every 7–10 days during the growing season. Alternate between a balanced fertiliser and a bloom booster for best results.

Q: Can I use slow-release pellets for begonias?
It’s not recommended. Slow-release granules can burn begonias’ shallow roots and don’t offer precise control. Liquid fertilisers are much safer and more effective.

Q: My begonia leaves are turning brown at the edges—what’s wrong?
This is often caused by calcium or magnesium deficiency, or salt build-up in the soil. Flush the pot and switch to a fertiliser with added CaMg.

Q: What’s the best fertiliser for tuberous begonias specifically?
Start with a 20-20-20 formula during early growth, then switch to 4-18-38 + CaMg once flowering starts to maximise bloom size and colour.