What Is a Good Fertiliser for Magnolia Trees?

Magnolia trees respond best to balanced fertilisers that provide steady growth without excessive leafiness. A good fertiliser for magnolia trees is one that delivers nitrogen for foliage, phosphorus for roots and flowers, and potassium for colour and resilience. In Australia, liquid or water-soluble blends work well for both young and mature magnolias.

Key Qualities of a Good Magnolia Fertiliser

Magnolias don’t need heavy feeding, but the right fertiliser makes a big difference to flowering and overall health. Look for these features:

Balanced NPK ratio: Equal or slightly higher nitrogen for steady leaf growth, plus phosphorus and potassium to support flowers.
Trace elements: Calcium, magnesium, and iron keep foliage deep green and healthy.
Gentle formulation: Magnolias prefer slow and steady feeding, not heavy chemical spikes.
Suitable for soil or pots: Liquid fertilisers are best for container magnolias, while water-soluble blends suit in-ground trees.

Quick answer: A complete, balanced fertiliser such as CompleteGrow NPK 20-20-20 Liquid is an excellent all-round choice for magnolias, while CompleteGrow 4-18-38 + CaMg supports buds and flowers during the bloom season.

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How to Use Fertiliser on Magnolia Trees

Applying fertiliser at the right time ensures nutrients go directly into growth and flower production.

Newly planted trees: Wait 4–6 weeks before fertilising, then apply a diluted balanced feed to help roots establish.
Young trees: Fertilise every 4–6 weeks in spring and summer to support steady growth.
Mature trees: Feed twice a year — once in early spring before blooming, and once in midsummer to maintain strength.
Potted magnolias: Use a liquid fertiliser every 3–4 weeks, as nutrients wash out of potting mix quickly.
Watering: Always water deeply after fertilising to prevent root burn and help nutrients soak in.

Tip: Apply fertiliser around the dripline (the area under the edge of the canopy), not against the trunk, where feeder roots absorb nutrients most efficiently.

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Aftercare, Mistakes to Avoid & FAQs

Good fertilising is only part of magnolia care. Combine it with watering, mulching, and correct pruning for the best results.

Avoid over-fertilising: Too much nitrogen produces leaves at the expense of flowers.
Mulch smartly: Apply a 5–7 cm mulch layer to conserve moisture and reduce nutrient loss.
Watch for leaf yellowing: Often a sign of iron or magnesium deficiency — a balanced feed will correct this.
Support blooms: Switch to a high-phosphorus, high-potassium fertiliser like CompleteGrow 4-18-38 + CaMg before and during flowering.

Magnolia Fertiliser FAQs

Q1: What is the best fertiliser for magnolia trees?
A balanced product such as NPK 20-20-20 is ideal for overall health. For flowers, add a phosphorus and potassium-rich blend like 4-18-38 + CaMg.

Q2: How often should I fertilise magnolias?
Young trees: every 4–6 weeks in spring–summer. Mature trees: twice yearly, in early spring and midsummer.

Q3: Can I use lawn fertiliser on magnolias?
No — lawn fertilisers are too high in nitrogen, which can reduce flowering.

Q4: Do magnolias in pots need different fertiliser?
Yes. Use liquid fertilisers more often, as nutrients leach quickly from potting mixes.

Q5: Should I fertilise magnolias in winter?
No. Magnolias are dormant in winter. Wait until spring growth starts.