How Do I Use Mycorrhizal Fungi for Hedge Plants?

What are mycorrhizal fungi?

Mycorrhizal fungi are beneficial fungi that form an association with plant roots. The plant supplies sugars to the fungi, while the fungal strands extend into the surrounding soil and help the plant access moisture and nutrients from a wider area than its roots could reach alone.

A product such as Rootgrow Mycorrhizal Fungi introduces suitable fungi directly to the root system when a hedge is planted.

It is best regarded as an optional establishment aid. It does not replace preparing the soil, planting at the correct depth, keeping roots moist before planting or watering the hedge properly afterwards.

How should mycorrhizal fungi be applied to different hedge root types?

The fungi need physical contact with living roots. The application method therefore changes according to how the hedge plants have been supplied.

Bare-root hedge plants

Bare-root plants are supplied without a pot or surrounding root ball. A dipping gel is the most effective way to distribute the fungi across the exposed roots.

1. Prepare the planting trench before mixing the gel.
2. Add the quantity of water stated on the gel sachet to a clean bucket.
3. Stir in the gel powder and allow it to thicken for the time stated in the instructions.
4. Add the mycorrhizal granules and mix until they are evenly suspended.
5. Dip the roots so they receive an even coating.
6. Allow excess mixture to drain back into the bucket.
7. Plant the hedge immediately.

The amount of water and product varies between pack sizes, so follow the instructions supplied with the exact pack rather than using a general recipe. Manufacturer instructions for the gel products normally require the prepared roots to be planted immediately after dipping.

Only dip a manageable number of plants at a time. Bare roots should not be left exposed to wind or sun while the remainder of the trench is prepared.

Pot-grown and cell-grown hedge plants

Water dry pot-grown root balls thoroughly before planting.

Remove the pot and inspect the root system.

Measure the recommended quantity of granules and distribute them across the part of the planting hole where the roots will sit. Place the root ball directly onto the granules so the outer roots make contact with the product, then backfill and water thoroughly.

Do not mix the granules through a large volume of loose soil. This can leave much of the product beyond the reach of the roots.

Root-balled hedge plants

Prepare a hole or trench that is wide enough to accommodate the root ball without forcing it into a confined space.

Apply the granules beneath and around the outer root area, following the rate for the size of plant being installed. The objective is to place the product where new roots will emerge from the root ball into the surrounding soil.

Do not put the granules in a deep layer at the bottom of an oversized hole. If the roots cannot reach the product, the fungi cannot form the intended association.

Instant hedging

Instant hedge units have a larger continuous root system. Apply the measured product along the prepared trench where the base and sides of the root mass will make contact with it.

Large instant units also require careful soil preparation and reliable watering. Plan the irrigation before installing the hedge where possible, as reaching the full root area becomes more difficult once the units are in position.

For the complete planting sequence, see our guide to planting a hedge.

When should mycorrhizal fungi be applied?

Apply the product during planting, immediately before the roots are covered with soil.

Standard planting granules should not simply be spread over the soil surface after the hedge has been planted. Without direct root contact, the application is unlikely to provide the intended treatment.

Mycorrhizal fungi are normally used as a one-off planting treatment rather than something that must be reapplied every spring. They should not be confused with hedge fertiliser, which supplies nutrients and may be applied later where the soil and condition of an established hedge indicate that feeding is useful.

How much mycorrhizal fungi should I use?

There is no reliable single rate for every hedge. The quantity depends on:

• the product and pack size
• whether the plants are bare-root, pot-grown or root-balled
• the height and root size of each plant
• the number of plants being installed
• the length and planting density of the hedge

Use the application table on the exact product packaging. Small cell-grown or 2-litre plants require considerably less product than large pot-grown or root-balled plants.

Hedging Plants Direct supplies Rootgrow in different pack sizes for domestic hedges, longer planting runs and trade or commercial projects. Calculate the number and size of plants before choosing the pack, then check the manufacturer’s rate against the final planting plan.

Can I use mycorrhizal fungi with compost?

Mycorrhizal fungi can be used alongside suitable soil preparation, but the two products perform different jobs.

A soil improver such as Hedge Planting Compost may help improve soil structure and moisture retention where the existing ground needs additional organic matter.

Mix the soil improver through the excavated soil rather than filling the planting trench with pure compost. Position the mycorrhizal fungi separately where they will touch the roots.

Good drainage must be addressed before planting. Neither compost nor mycorrhizal fungi can correct a trench that continually fills with water.

Can I use fertiliser at the same time?

Avoid placing concentrated fertiliser directly against newly planted roots. Strong or phosphorus-rich fertilisers may also interfere with the formation of mycorrhizal associations.

During early establishment, concentrate on:

• correct planting depth
• suitable drainage
• thorough initial watering
• keeping grass and weeds away from the root area
• checking moisture below the soil surface

Feeding can be considered later if the hedge species, soil and plant condition indicate that it is needed. More fertiliser does not automatically produce faster or healthier establishment.

Is standard Rootgrow suitable for every hedge plant?

Standard Rootgrow is suitable for most common hedging plants, trees and shrubs, but it is not the correct formulation for every plant.

The manufacturer states that standard Rootgrow is not suitable for rhododendrons, azaleas, heathers, blueberries or cranberries. These acid-loving plants require an appropriate ericoid mycorrhizal product. Check the product label if you are planting an ericaceous hedge or an unusual species.

What mistakes should I avoid?

The most common application mistakes are:

• scattering the granules over the soil after planting
• placing the product too far beneath the roots
• mixing it throughout a large volume of backfill
• preparing bare-root plants before the trench is ready
• allowing dipped roots to dry before planting
• using an unsuitable formulation for an ericaceous plant
• treating mycorrhizal fungi as a replacement for watering
• adding more than the stated rate in the belief that more will work better

Mycorrhizal fungi can support establishment, but the fundamentals still decide whether a hedge succeeds. Prepare a wide enough planting area, keep the plants at their original growing depth and water the complete root zone thoroughly after planting.

Our Planting Essentials guide explains how Rootgrow, soil improvement, irrigation and plant protection fit into the wider hedge-planting process.