All About Worms

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Welcome to Northern Gardening!
Hosts Joan Farnam and Paula Sundet-Wolf hosted this month’s program with guests:
Ann Russ, local gardener and retired teacher who talks about using vermiculture in the classroom,
Kent Jones, local gardener, who talks about his experiences with worm composting and worms in the garden and
Cindy Hale, scientist with NRRI (Natural Resources Research Institute) in Duluth who talks about her research on earthworms and what is happening in our local forests.

Northern Gardening airs on the second Thursday of every month and is hosted by Cook County Extension and the Northwoods Food Project. It is also rebroadcast at 6 a.m. on the 2nd Saturday morning of the month.
Northern Gardening airs on the second Thursday of every month and is hosted by Cook County Extension and the Northwoods Food Project. It is also rebroadcast at 6 a.m. on the 2nd Saturday morning of the month.

Gardeners have been told for years that worms are great for the soil and they have some wonderful attributes they bring to the garden. Composting bins for worms or vermicomposting has exploded in the gardening realm and many gardeners use vermicompost as part of their starting media for plants or as a gardening additive.

• There are approximately 4,500 species of worms in the world and of those, about 2,500 are earthworm species.
• Minnesota has at least 15 species of earthworms.
• Earthworms are either earthmovers or composters.
• They tend to be solitary species with tunnel through the earth, aerating, decompacting and mixing soil strata and thus making surface nutrients available to plant roots at lower levels. Good for gardeners / not so good for native plants growing in our forests.
• Composters live in organic matter on the soil surface where they consume bacteria present in dead vegetation, animals and manure, turning it into humus.

Are earthworms native?
• Any native North American species of earthworms that may have been living here were destroyed when glacial ice sheets covered Minnesota. So our local forests evolved without an earthworm population.
• Earthworms were brought over in the 1800’s by settlers who brought plants with them from Europe. Earthworm egg cases were probably brought in with the plants.
• Ships would also use soil and rocks as ballast that would be dumped on shore when they adjusted the ballast for the ship.
• Recently, using worms as fishing bait has also increased their populations in forested areas. Unused fishing bait is often dumped out rather than taken back home. Road building activities that move dirt, vehicle tire treads can carry egg cases with them, etc.
• Without humans moving them, earthworms can move only about mile in only about 100 years.

Specific species of earthworms are causing damage in the forest
• Earthworms that are being found in hardwood forests can cause forest decline because they change the ecosystem substructure that many forest plants rely upon.
• If you don’t have earthworms in your annual leaf litter, decomposition is controlled by fungi and bacteria. Decomposition is much slower and the result is a thick, spongy forest floor called a “duff” layer. This layer can be 4-5” thick in very rich sites. This duff layer is essential for some understory plant species to survive. Small tree seedlings and understory plants have their root systems in this duff layer and are able to survive.
• When earthworms are introduced into this layer, decomposition occurs much faster and the duff layer pretty much disappears. They also mix the organic layer with the mineral soil layer. This has resulted in small tree seedlings not being able to germinate and survive. Additionally, many of the understory plant species cannot survive. This then has a domino effect leading to the loss of cover for ground nesting birds, small mammals, amphibians and reptiles, insects and spiders. Primary habitat and food sources are lost.
• Different invasive earthworms species have different habitat/feeding preferences (belong to different “functional groups”) and thus different impacts on the ecosystems into which they spread or are introduced. Different combinations of species can result in different impacts as well (Hale et al. 2008).

Boreal forests and earthworms
• Boreal forests composed of pine (Pinus sp.) and spruce on sandy and / or acidic soils are likely to be more resistant to invasion, as they have been in northern Scandinavia despite the presence of lumbricids for thousands of years.
• The presence of deciduous tree species with low C:N ratio litter, such as aspen and birch mixed with pine and spruce is likely to allow earthworms to inhabit a site, especially those species such as Dendrobaena octaedra.
• The rate and magnitude of the removal of the forest floor and consequences for native forest plant communities depends upon the species of earthworms invading.

Ann Russ set up a worm composting bin in her classroom.
The worms that are used by most worm composters are called red wigglers or are the species Eisenia fetida. These cannot survive our winters here if they are released into the outdoors. Since the decline of horses in agriculture, most populations are in artificial situations.
Lumbricus rubellus is being used in vermicomposting now, too. A population of L. rubellus can consume 10 cm or more thickness of intact forest floor within one growing season, which is faster than plants rooted in the forest floor can adjust, resulting in increased plant mortality during initial invasion.

Things to make us feel better:
• Most of us did not import these earthworms into our garden, they pretty much were already there in the soil when we started gardening. (We can blame our ancestors!)

• Earthworms: Their primary food source is bacteria, although they will eat fungi, nematodes, protozoa and organic matter on or in which these microorganisms live. Worms can live for 15 years. They shred organic matter, aerate soil, aggregate soil particles and move organic matter and microorganisms in the soil. Vermicastings(worm poop) are 50 percent higher in organic matter than soil that has not moved through worms. Worms’ digestive enzymes unlock phosphate and other nutrients making them available for plants.

They do great things in our agriculture soils.
• One study has shown that each year on an average acre of cultivated land, 7,200 kg of soil can pass through earthworms and be deposited atop the ground — almost double that amount can be moved in really wormy soil. 

How do I know if I have a good soil food web present in my soil?
• If you have 5 – 30 earthworms in your garden soil in a square foot.
• Set a soil trap. Bury a quart sized container in the soil so that the lip of the container is at the ground level. Put an umbrella over it or something to keep the rain out but keep it open at the soil level. Add a couple of moth balls. Leave alone for 3 – 7 days. Check to see what you have in your trap. If your soil is pretty good, you will have centipedes, millipedes, other macroarthropods.

TIPS to be responsible with your gardening when it comes to earthworms, etc.:
• Keep your gardening/agriculture soil totally separate from your forest soils.

• Don’t bring in soil from another location like down south that may contain egg cases for earthworm species you don’t already have in your garden.

• If you are using vermicompost, make sure if you are using it outside in your garden that you know exactly what species of earthworm you have present. Sometimes when you order a vermicomposting kit you can still have egg cases from other species present that you don’t know. It could be a species that may be harmful if it escapes into other forested areas.

• Don’t take garden soil from your garden and dump it into the woods. The same would be true with potted plants. Be very careful what you do with soil that comes in potted plants from other places.

• Don’t dump your leftover fish bait (worms) you have purchased into your garden or onto the forest soil or into a lake, hoping they’ll drown. They won’t, and you will have introduced them to that area.

Extension Updates: Variegated cutworm:
We are starting to see some of the larger cutworm larvae stages feeding on different plants in our gardens this year. Holes in potato leaves, broccoli leaves, pea and bean stems cut through could be due to cutworm larva.
• You can wrap several layers of newspaper around the stems of your plants about 1 to 1/5” below the soil and the same above to prevent the cutting off of the main stem by a cutworm larvae. Tinfoil will also work as will cardboard if it is close to the stem.
• You can spray or dust your leaves with a garden product like Thuricide or Dipel that contains Bt (bacillius thuriengensis) or Btk (bacillius thuriengensis var. kurstaki) as the active ingredient. This is a bacteria, ingested by a susceptible caterpillar, that will release a crystalline protein called an “endotoxin” that poisons the insect’s digestive system. Eventually holes in the caterpillar’s gut allow digestive juices to leak through the holes and cause a general infection that kills the insect.

Advantages of using Bt or Btk:
a. Caterpillars that die after ingesting Bt or Btk are not considered dangerous to birds or other animals that feed on them.
b. Generally, sunlight and other microbes destroy Btk applied to foliage, so Btk does not multiply or accumulate in the environment.
c. Btk does not appear to post any significant threat to human health or to pets.

Flea Beetle Damage:
Use a floating row cover to exclude flea beetles from your crops. You can also plant a ‘trap’ crop. They absolutely love radishes and / or arugula. They will then leave some of the other plants alone and simply ‘nosh’ on the arugula.

Announcements:
Cook County Extension office located in the CC Community Center building in Grand Marais does have soil testing available through the University. We do recommend a soil test before you start adding amendments to your soil. We also have an animal husbandry and gardening library available for folks who would like to check out more specific information on topics we discuss on Northern Gardening.
Cook County Master Gardeners will be planning a container gardening contest this summer with prizes and a local garden tour on Saturday, August 18th. So if you are a gardener and would like to enter either your garden as an example of how people can grow in small spaces using containers or small raised beds, pick up entry forms and fill them out by July 18th.
Entry forms can be found at the CC Extension office as well as on posters hanging up around town.

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