Can You Use Mycorrhizal Fungi and Fertilizer Together?

If you're already using fertilizer in your garden, you might be wondering: Can I add mycorrhizal fungi too, or will one interfere with the other?

The short answer is yes, mycorrhizal fungi and fertilizers can be used together. In fact, they serve different purposes in plant nutrition.

Fertilizers supply essential nutrients, while mycorrhizal fungi help plant roots explore more soil and access nutrients already present.

But there's an important detail: how much fertiliser you apply, particularly phosphorus, can influence how well mycorrhizal fungi establish and function. Here's how to make the most of both.

1. What's the Difference Between Fertilizer and Mycorrhizal Fungi?

Think of fertilizer as a source of nutrients and mycorrhizal fungi as a partner that helps your plants access them.

Fertilizers  provide nutrients such as nitrogen (N), phosphorus (P), and potassium (K), which plants need for healthy growth, root development, flowering, and fruit production.

Mycorrhizal fungi  are beneficial microorganisms that form a natural partnership with plant roots. Their microscopic filaments, called hyphae, extend into the surrounding soil, reaching areas beyond the roots themselves.

This extended network helps plants access phosphorus, certain micronutrients, and water. In return, plants provide the fungi with sugars produced through photosynthesis.

2. Can Fertilizers Harm Mycorrhizal Fungi?

Yes, excessive fertilisation can interfere with mycorrhizal activity, particularly when soil phosphorus levels are already high. When plants have plenty of readily available phosphorus, they may rely less on their fungal partners, reducing mycorrhizal colonisation. However, this doesn't mean you should avoid fertilisers altogether. The key is to apply nutrients according to your plants' needs rather than overfeeding them. Balanced fertilisation and mycorrhizal fungi can work together in a healthy garden.

3. Which Fertilisers Can You Use With Mycorrhizal Fungi?

Different fertilisers can be used alongside mycorrhizal fungi. The important factors are nutrient concentration, application rate, and your soil's existing fertility.

Fertilizer Type	Compatible with Mycorrhizae?	Practical Advice
Organic fertilizers	Yes	Apply according to plant needs and avoid excessive phosphorus.
Compost	Yes	Mature compost supports soil fertility and structure.
Slow-release fertilizers	Yes	Provide nutrients gradually when used at appropriate rates.
Water-soluble fertilizers	Yes	Follow recommended concentrations and avoid overfeeding.
High-phosphorus fertilizers	With care	Excess phosphorus may reduce fungal colonization.

Organic fertilisers aren't automatically better for mycorrhizae than mineral fertilizers. What matters most is providing the right nutrients in the right amounts.

4. How to Use Mycorrhizal Fungi and Fertiliser Together

Combining mycorrhizal fungi with your regular feeding routine is simple. Follow these four steps to support healthy roots and nutrient uptake.

Step 1: Apply Mycorrhizal Fungi Near the Roots

Transplanting is an excellent opportunity to introduce mycorrhizal fungi. Apply your inoculant directly to the root ball or planting hole so the fungi can make contact with living roots.

Step 2: Water After Planting

Keep the soil evenly moist while plants establish. Avoid waterlogging, which can limit root function and beneficial microbial activity.

Step 3: Fertilise According to Plant Needs

Use an appropriate fertiliser at the recommended rate. If your soil already contains sufficient nutrients, additional feeding may not be necessary.

Step 4: Support the Root-Zone Environment

Add mature compost when needed, reduce unnecessary soil disturbance, and maintain good drainage. These practices help create favourable conditions for roots and beneficial microorganisms.

You generally don't need to wait several weeks between applying mycorrhizal fungi and fertilizer. The most important consideration is avoiding excessive nutrient levels during fungal establishment.

5. Do You Still Need Fertilizer If You Use Mycorrhizal Fungi?

Mycorrhizal fungi don't replace fertilizers, but they can help plants use available nutrients more efficiently.  Their fungal networks extend beyond the roots, helping plants access phosphorus and other nutrients from a larger volume of soil. However, they don't create nutrients, so plants growing in nutrient-deficient soil may still need fertilizer. The best results come from combining beneficial fungi with balanced soil nutrition.

6. Can You Use Mycorrhizal Fungi and Fertilizer in October?

Yes! Fall can be a great time to introduce mycorrhizal fungi, especially when transplanting perennials, shrubs, fruit trees, or cool-season vegetables. As long as plants have living, active roots and soil conditions are suitable, mycorrhizal fungi can establish and support nutrient uptake. However, autumn fertilisation should depend on what your plants actually need, since many plants require less feeding as growth slows.

Curious what happens to these fungi during colder months? Read our guide: What Do Mycorrhizal Fungi Do in Fall?.

7. Support Your Plants With GrowMate Rootmax

GrowMate Rootmax contains Rhizophagus irregularis, an arbuscular mycorrhizal fungus that forms beneficial partnerships with many common garden plants. By extending the effective reach of the root system, Rootmax helps plants access water and nutrients, particularly phosphorus, from the surrounding soil.

Rootmax can be incorporated into gardening programs that use organic or conventional fertilizers, making it a useful addition to your regular plant-care routine.

How to apply:  During transplanting, apply 5 g of Rootmax per plant, placing the powder directly in contact with the roots or in the planting hole before watering.

Rootmax is suitable for many vegetables, flowers, herbs, and other compatible garden plants.

Learn more about applying mycorrhizal fungi for root growth.

Frequently Asked Questions

Can I apply mycorrhizal fungi and fertilizer on the same day?

Yes! You can apply both on the same day. Place the mycorrhizal inoculant near the roots and apply fertilizer at an appropriate rate.

Can I use mycorrhizal fungi with liquid fertilizer?

Yes, they can be used in the same gardening program. However, mixing them directly in one container depends on the specific products and their formulations.

Does phosphorus fertilizer kill mycorrhizal fungi?

Not necessarily. Excessive phosphorus availability can reduce mycorrhizal colonization because plants become less dependent on their fungal partners.

Can mycorrhizal fungi reduce how much fertilizer I need?

They can improve nutrient uptake and may help plants make better use of available nutrients. However, fertilizer requirements still depend on soil fertility and plant needs.

Do all garden plants benefit from mycorrhizal fungi?

No. Many vegetables, herbs, flowers, and fruit plants form mycorrhizal partnerships, but members of the cabbage family, including broccoli, cauliflower, and kale, generally do not.