SEASONED gardeners will tell you that having earthworms in the garden is good for the soil. Earthworms tunnel through the soil improving drainage and aeration as they go.

They move nutrients to deeper levels in the soil by taking organic material deposited on the surface to lower levels; they breakdown organic matter from large complex molecules into smaller, simpler molecules that a plant can use.

Seasoned gardeners will also know that you can measure the fertility of your garden soils by counting the earthworms.

Measure the fertility of your soil by digging out a cube of soil (30x30x30 centimetres) and count the earthworms you find.

If you find 10 or more earthworms your soil is fertile and healthy. If you find fewer than 10 earthworms, you may want to consider improving the fertility of the soil to encourage earthworms.

How to encourage earthworms in the garden.

If your garden has very few or no earthworms, you may need to introduce earthworms to get a population started.

The best way to move earthworms into your garden soil is to dig up large chunks of soil rich in earthworms and worm burrows and set them whole in your garden so new earthworm colonies can get started. Choose soil of a similar type to where you want to introduce the earthworms.

Lawn clippings enhance the habitat for earthworms and beneficial micro-organisms.

Earthworms ingest the clippings at night, helping increase the aeration and fertility of the soil, and in the process maintain a thatch base in lawns making the lawn feel springy when walked on.

If too much thatch is removed, worms will migrate to other more favourable habitats. If the worms migrate or are killed, a deep thatch can result, causing the lawn soil to become compacted and less fertile.

Where the earthworms feed, and how they improve the soil depends on the species. For example do not move earthworms from your compost heap to the garden, they don’t like it – there’s not enough organic matter – so it’s best to leave the stripy red earthworms that live in compost in the compost and leave soil earthworms that like eating soil in the soil and surface-dwellers that like eating organic matter in the surface. Leave earthworms in their respective habitats.

If there are few or no earthworms in your garden soil it could mean that the soil is compacted, low in organic material or too acidic.

Fork and loosen the soil and add organic material such as grass clippings, compost or animal manure to the soil; these will help earthworms thrive. Make sure the pH of the soil is above 4.5; add lime if the pH is below 4.5.

Worms can lose up to 20 percent of their body weight each day in mucus and castings, so they need moisture to stay alive.

Groundcover reduces moisture evaporation and decaying organic matter (humus) holds moisture in the soil. In dry spells, some species burrow deep into the soil and are inactive until rain “reactivates” them. So, keep the soil well-watered deep down by irrigating in dry periods.

Water long and slow so that the water penetrates deep in the soil where it is more beneficial to the earthworms and does not evaporate off so quickly.
Keep those earthworms tunnelling.

Common earthworms in NZ

n Grey earthworms (Aporrectodea caliginosa) are the most common earthworm in New Zealand. The most common others and how to identify them, include:

  • Blue-grey worm (Octolasion cyaneum) lives in topsoil, about spade depth. Fat, blue-grey body; yellow tip on tail; yellow ring on neck.
  • Grey worm (Aporrectodea caliginosa) lives in and eats garden soil. Pink-grey body, dark pink head, up to 15cm long.
  • Dung worm (Lumbricus rubellus) lives in organic matter, especially cow pats. Brown body, red saddle, 3-10cm long.
  • Tiger worm (Eisenia fetida) lives in/eats organic matter, leaf litter and compost. Bright red body with yellow stripes, up to 13cm long, pictured.
  • Nightcrawler (Lumbricus terrestris) lives up to 3 metres deep in soil in North Island. Very large (up to 30cm); red-brown body; flat tail.
  • Black-headed worm (Aporrectodea longa) lives deep in soil, mostly in North Island. Large (9-12cm); dark grey-brown body.

April is the best planting month


THE heat of summer is fading and almost forgotten; the soil is cool and moist; the weather is mild and it’s a pleasure to get out into the garden.

This is why April is one of the best months to put in new plants and to dig rootbound potted plants into the open garden. They appreciate the milder conditions and have time to settle in before the cold of winter hits.

Tips for planting:

Before planting you have a great opportunity to improve the soil. Dig in well aged compost and add some organic sheep pellets blending these goodies into an area that is more than twice the width of the pot you are removing the plant from.

Dig a hole about twice the size of the width of the plant pot and approximately the same depth. Heap the removed soil to the side of the planting hole.

Water the plant in the pot and leave it to drain. Water the planting hole too, and allow the water to drain away until the soil is just moist.

Take the plant out of the pot, which may be a bit more difficult than you anticipated especially if the plant has been in the pot for a while. The roots may be clinging to the sides, making it difficult to remove.

Running a knife blade down the side between the pot and the mix may help as will putting the pot on its side and gently rolling it backwards and forwards on a hard surface with a bit of pressure on it to help loosen the plant’s soil and root system.

Remove the plant from the pot and inspect the root system. If the plant is potbound the roots will be seen circling around the outside of the rootball. Loosen these gently with your fingers or use secateurs to cut the encircling roots.

Sit the plant in the prepared hole and adjust it to ensure it won’t be sitting any deeper than before. Fill the soil back in around the rootball and water well making sure that the water soaks right through to the root area.

If the rootball was well compacted it will be naturally water repellent so it is important to ensure the water doesn’t just run away to the sides.

Building a raised ring of soil (like a volcano crater) around the new plant will help direct water to the roots, but don’t overdo it and create a bog.

Fertilise in the spring as new growth appears.

You can plant most evergreen shrubs and trees in April (except the cold-sensitive), grassy

plants and strap-leafed varieties.

Don’t forget too, that April is the month for planting spring flowers and bulbs.