How Much Mycorrhizal Fungi Should I Use?

Why does the amount of mycorrhizal fungi vary?

Mycorrhizal fungi products are applied to the root system rather than measured simply by the length of the hedge. A small bare-root whip requires much less product than a large root-balled plant, tree or mature section of instant hedging.

The quantity you need will therefore depend on:

• The number of plants being installed
• The height and size of each root system
• Whether the plants are bare root, cell grown, pot grown or root balled
• The application rate printed on the particular pack
• Whether the granules are being used dry or mixed with the supplied dipping gel

A pack should be treated as covering an approximate number of plants rather than an exact length of hedge. Two varieties sold at the same height can have noticeably different root systems.

Rootgrow quantities for bare-root hedging

For bare-root plants, Rootgrow can be mixed with the supplied gel to create a dipping solution. The manufacturer’s current guidance gives the following approximate coverage rates.

These figures are useful for planning, but they remain approximate. Species with broad, fibrous or unusually large root systems can use more dipping solution than plants with smaller roots.

How to apply it to bare-root plants

Prepare the dipping gel according to the instructions supplied with the pack. Stir the granules through the prepared gel so they remain distributed throughout the mixture.

Open one bundle of plants at a time and keep the remaining roots covered. Dip the root system into the mixture, allow excess gel to drain back into the bucket and plant immediately. The roots should receive an even coating without being left exposed to wind or sun while other work is completed.

How much should I use for pot-grown hedging?

The amount required for pot-grown plants is normally based on the volume of the container or root ball.

As a broad guide, the manufacturer states that a 360g pack can treat up to 19 plants in 2-litre pots or one root system of approximately 100 litres. A smaller 60g pack is described as treating up to six 2-litre pots or one 10-litre pot.

Larger pot-grown hedging may therefore use considerably more product per plant than small 2-litre stock. Check the plant’s actual pot size rather than estimating the quantity from its height alone.

How to apply it to pot-grown plants

Measure the recommended amount and sprinkle the granules evenly into the planting hole where the outer roots will touch them.

Position the root ball directly over the product and backfill the hole normally. Do not scatter all the granules over the soil surface or mix them through a large volume of backfill where only a small proportion will contact the roots.

How much should I use for root-balled or instant hedging?

Root-balled plants and instant hedging can have much larger root systems than ordinary pot-grown plants. The amount needed should be based on the approximate root-ball volume and the instructions provided with the pack.

Apply the granules beneath and around the sides of the root ball so that newly developing roots can contact the fungi. Do not place the entire quantity at the bottom of an unnecessarily deep hole.

For a large planting scheme, calculate the number and sizes of the plants before ordering. The current Rootgrow Mycorrhizal Fungi with Gel range includes 360g, 1kg and 2.5kg options for different project sizes.

Is using more mycorrhizal fungi better?

Applying more than the recommended amount is not a substitute for placing it correctly. Direct root contact is more important than scattering a large quantity around the planting area.

Mycorrhizal fungi also do not compensate for:

• Dry or damaged roots
• Poorly prepared or compacted soil
• Incorrect planting depth
• Waterlogging
• Insufficient watering after planting
• Heavy weed or grass competition

HPD advises that Rootgrow should be placed directly against the roots and that it does not replace good soil preparation, correct planting depth or regular watering.

Can mycorrhizal fungi be applied after planting?

The best opportunity to apply Rootgrow is while the roots are exposed during planting. This makes it possible to place the product directly against the root system.

Simply scattering granules over the surface of an established hedge is unlikely to provide the same level of root contact. If a hedge has already been planted, concentrate first on appropriate watering, weed control, mulching and correcting any planting or drainage problems.

Is standard Rootgrow suitable for every plant?

Standard Rootgrow is suitable for most hedging plants, trees, shrubs and roses. However, the manufacturer states that the standard product is not suitable for rhododendrons, azaleas, heathers, cranberries or blueberries. A specialist ericoid formulation is recommended for relevant acid-loving plants. It is also unsuitable for brassicas.

Always check the current pack instructions where the planting includes an unusual species or a mixture of hedging and ornamental plants.

Which pack size should I choose?

Choose the pack by counting the plants and recording their sizes or pot volumes.

A 360g pack is generally suitable for a modest domestic hedge or a smaller planting project. A 1kg pack is more economical for a long run of bare-root hedging, while the larger 2.5kg option is intended for substantial garden, landscaping, trade or commercial planting schemes. Hedging Plants Direct currently supplies all three sizes.

Allow a sensible margin where the plants have particularly large roots, but avoid buying purely on hedge length without checking the root type and size.