November 2018 – The Garden Professors™

“Fun-guy” in your Mulch

By Jim Downer

As many avid GP readers are aware, mulches are a common horticultural tool that help gardeners maintain soil moisture, nutrient content, weed suppression and assist in disease prevention. The best mulch is made from chipped tree trimmings wastes and has a large wood content. Coarse “arborist chips” mulch is fast becoming one of the most frequently sought after mulches for residential landscapes. It is very effective and contributes to significant soil improvements over time. As chip mulches decompose, the fruiting bodies of fungi are often seen growing up through mulch. Sometimes, as gardeners work in previously mulched beds, they see mycelium or cordons (rhizomorphs) of mulch fungi growing through the mulch. Some gardeners are not fond of finding mushrooms growing in their mulch and have termed these as “nuisance fungi”. There have even been extension leaflets on nuisance fungi and how to rid them from your garden!! Fungi are a natural part of mulch breakdown and their presence in mulches is desirable!

*Phanaerochaete chrysorhiza* invading *Eucalyptus globulus* mulch

The first encounter many gardeners have with mulch fungi is when they see “mold” growing in the chips or at the interface of mulch and soil. Mold gets a bad rap with many homeowners when they find it after water damage in their house, so perhaps they assume it is also bad for their gardens. Mold abatement in homes has become a specialized industry, and while the spores of some fungi can be human pathogens, fungi are not to be feared in gardens unless your immune system is damaged or otherwise compromised. Unlike houses, gardens are a good place for fungi to grow and thrive.

Fungi absorb water and nutrients from their hyphae which grow into their food (mulch particles). The absorptive lifestyle of fungi is unique. Since fungi have no internal digestive systems, they rely on excreting enzymes outside their bodies and into their food which breaks down the substrate so they can absorb it. By doing so, they also release minerals, sugars, amino acids and many other compounds for other microbes and plants to utilize. Fungi are mostly saprophytes or decomposers, and their role is to release organic nutrients to soil so they can be recycled. This is why mulches are so beneficial to woody plants. Without fungi, forest litter would pile up largely undecomposed because bacteria and other microbes are less efficient in breaking down cellulose. Some fungi are mutualistic partners with woody plant roots. Ectomycorrhizal (EM) fungi rely on interactions between trees themselves and the litter or mulch layers under trees. Fruiting bodies of EM fungi may appear as mushrooms or puff balls in or next to mulches.

*Lepiota* spp. an ectomycorrhizal species

*Amanita muscari* , another ectomycorrhizal species. Just don’t eat it.

Sometimes fruiting bodies (mushrooms) push through mulch, but are not the result of mulch presence. Pathogens such as Armillaria mellea (oak root fungus) can form through mulch layers or turfgrass, but they are fruiting off the dead roots of their tree host. Similarly, the inky cap mushrooms (Coprinus spp.) often grow saprophytically on dead roots (they are not the cause of root death) and will push through litter layers. Coprinus are good indicators that a tree has dead roots. Coprinus is not a plant pathogen, and mulch does not increase prevalence of pathogens in landscapes. As we have discussed many times in the blog, mulches are unlikely to spread or support plant pathogenic fungi.

*Coprinus* spp., which feed on dead roots

Another way to view the role of fungi is the chemistry that they facilitate in soil. Mulch is organic matter, which has a high concentration of carbon. Carbon is transformed from a solid form into a gas – carbon dioxide – through the action of microbes (mostly fungi). So oxidation of carbon is driven by fungi growing through their substrate (forest litter in forests or mulch in gardens). In mulching systems this is a slow process taking a few years. In composting systems it is rapid, taking months with the added energy of mechanical turning etc. Slow decomposition of organic matter is useful, as the benefits of mulch in suppressing weeds, slowing evaporation from soils etc. are maintained over time. Slowly oxidizing carbon means that it will be around longer, creating less greenhouse gasses than in the composting process.

In publications that recommend ways for “dealing with nuisance fungi” it is suggested to let mulch dry out, which stops the action of the fungi. This is one of the most harmful things that can be done for active mulch zones. Killing the fungi in mulch also stops their oxidation of carbon, subsequent nutrient release and support for the high microbial activity in mulches that benefit both plants and disease suppressing fungi that plants rely upon to maintain their health. While fungi can reactivate when dry mulches are moistened, their biomass is damaged by severe drought which also injures plant roots as well.

All good things come to an end or as our physics friends say, “Entropy increases!!” So as labile (easily metabolized) carbon is used up in fresh mulches, fungi go into spore bearing or reproductive phases and begin to make fruiting bodies. As long as there is labile carbon, fungi will thrive and grow mycelium and hyphae into their food. When carbon is being used up (or when there is sufficient mycelium), fruiting bodies start to form. To maintain these processes, it is important to add fresh mulch over the old decaying mulch. Once or twice a year depending on temperature and moisture levels. Along the way, some mulch may develop fungal fruiting bodies. Fruiting bodies may resemble mushrooms, puff balls, earth stars, bird nest fungi, or simply resemble paint that has been splashed on the wood chips. They are only trying to survive by developing spores which will later spread onto fresh mulch materials. Most mulch fungi have very ephemeral fruiting bodies, so even if they are seen to be a “nuisance”, they will only be around for a very short time before they also decompose and become part of the remaining mulch layer or soil.

*Ceraciomyces tessulatus*, a paint-like fungus

One very common group of organisms seen in mulch and mistaken for fungi are the slime molds. They are not related to fungi, but do develop spores and have a mobile (plasmodium) phase where they can be seen to slowly move from one spot to another. Eventually, when the plasmodial stage is done feeding, the sporangial phase is made and they turn into spores. The most commonly encountered slime mold in mulch beds is the dog barf fungus, a slime mold called Fuligo spetica. Fuligo is dramatic because it can appear overnight and is large (a patch of the sporangium can be several inches across). When kicked, Fuligo bursts into dark spores that will fly up into the air. Slime molds are also saprophytes and live on the decomposing organic matter in mulch. They pose no threat to humans or garden plants.

Yellow slime mold, aka dog vomit fungus (photo from Wikimedia)

Fungi in the mulch are a good thing and indicate that moisture, temperature and organic matter are at the correct levels for high microbial activity! This is what creates a healthy soil and ensures healthy garden plantings.

Thanksgiving: A celebration of the native plants and indigenous crops that grace the table

Native vs. non-native – that a subject that is brought up frequently on our forums and one we have to discuss at length. However, I thought I’d take it from a different direction this week, a little diversion if you will, seeing as we are just a week away from our American celebration of Thanksgiving that centers around food – much of it native to the United States.

It is a holiday that is quintessentially American (or North American, since our Canadian friends also have their own Thanksgiving). A commemoration of not only the arrival and survival of the pilgrims in Plymouth in 1621, but of our thankfulness for what we have. It is a time for us to gather with family or friends and reflect upon our blessings.

While, much to my chagrin (and that of many others), Thanksgiving seems to have been swallowed up by the Christmas “season” and you can even go shopping for more stuff (an abomination, for sure) on a day when we are supposed to be thankful for what we have, it is still a day celebrated by many.

Turkey, dressing, potatoes, fresh bread rolls and pumpkin pie are the traditional fare for the celebration these days, but they are a far cry from what the original feast shared by the pilgrims and American Indians would have featured.

Historians agree that, while the feast was probably meat-heavy, turkey was probably not on the menu. It just wasn’t as popular a food item as it is today. Most agree that the original feast featured venison, with some waterfowl (goose or duck) and seafood (shellfish like oysters are a definite, maybe even eels or other shellfish).

I don’t think I’m alone in saying that I like the side dishes better than I like the actual turkey. There’s the dressing (or stuffing, depending on your preparation or colloquial terminology), mashed potatoes, sweet potatoes, and my aunt’s seven-layer salad that’s usually more mayo and bacon bits than vegetation.

The produce dishes at the first Thanksgiving would have been vastly different than the modern day smörgåsbord that we prepare. Experts agree that the majority of dishes would have been from native plants and indigenous crops grown by the local tribes, with a few ingredients showing up from the pilgrims’ gardens.

First off, the absence of wheat flour, sweetener and flour would mean the lack of the classic dessert…pumpkin pie. It is hard to imagine a lack of pumpkin while we live in a time in which we are surrounded by pumpkin spice everything (though mostly artificially flavored).

Sugar would have been too expensive to purchase for the voyage, and other sweeteners would have been limited to maple or other tree syrups. (Colonists had not yet brought over the honey bee, which is a European immigrant itself).

This is not to say that there wasn’t squash. There were squashes, including pumpkins, as part of the native diet at the time having spread from their origins in Mexico and Central America . They were likely included in the feast, but either boiled or roasted, and unsweetened.

Beans would have probably been one of the dishes, as well. The Natives Americans ate beans both in dry and green form, but at a fall feast, the beans were likely the dried variety and cooked into a soup or stew. Corn was also a feature of the first Thanksgiving, but not sweet corn (which didn’t make an appearance until much later). The corn would have been a flint type (similar to popcorn) that would have been cooked into porridge or used as a bread.

Native tree nuts, such as walnuts, chestnuts and beech nuts could have also been used in the preparation of dishes. There isn’t any written record of the native cranberry or blueberry being used, either, but they would have been abundant in the area. They likely wouldn’t have caught on in popularity until sweeteners such as sugar from Europe or honey was available to dull their acidic bite, but the dried fruits could have been used in preparations of some of the meat. If there was a salad, watercress could have been used if an early frost hadn’t wiped it out.

The pilgrims had brought with them from Europe various seeds, including herbs and onions, that could have been used to flavor some of the dishes. They may have also brought things like turnips and carrots that could have been available for the first feast (though there isn’t any direct written proof).

One native food that would have most likely been on the first Thanksgiving table is the sunchoke (Helianthus tuberosus), or Jerusalem artichoke. Fallen out of favor for some time, the sunchoke is making its return to many gardens.

Image result for jerusalem artichoke — Jerusalem artichoke/sunchoke flower *Wikimedia Commons*

A true native food source, the sunchoke is the tuberous root of a species of sunflower (you may even see them growing on roadsides in the fall). The rhizome is roasted or boiled and has a nutty, starchy, potato-like texture and flavor. If you want to grow it, just remember that it is a perennial that will readily spread in the garden. These would have been the closest things to a potato dish the first celebrants would have eaten — we were still a long way away from bringing the potato from South America and the sweet potato from the Caribbean. (Botanist’s note: What we eat are sweet potatoes [Ipomea batatas], not yams [Dioscorea sp.], despite the insistence of canning companies. They aren’t even in the same family.)

So as you sit down for your Thanksgiving feast, be thankful for the blessings in your life and for the leaps and bounds our food options have improved over the past 400 years. Also be thankful for butter, flour, and sugar so you can have your pumpkin pie.

Native vs. nonnative – can’t we all just get along?

Probably the most contentious gardening topic I deal with online is the native vs. nonnative plant debate. This, unfortunately, is a debate that is more based in emotion than science, and I don’t intend to stir that pot again. We’ve discussed it on this blog before (you can find a list of them here), and I’ve published both a literature review and a fact sheet on the science relevant to tree and shrub selection. What I want to do in this post is compare two research papers, both in peer-reviewed journals, that come up with dramatically different conclusions.

The first has been getting a lot of publicity on the web and in social media. It was published just two days ago, but because of widespread PR prior to release it appears over 37,000 times in a Google search. The title – “Nonnative plants reduce population growth of an insectivorous bird” – and much of the prerelease publicity about the article spells doom and gloom. It’s a message that gets traction.

The second was published a year earlier and is entitled “Native birds exploit leaf-mining moth larvae using a new North American host, non-native Lonicera maackii.” It appears 194 times in a Google search, even though it’s been available for over a year.

The reason I’m singling out these two articles is they have completely different messages – and one of them is not being heard as loudly as the other. The first focuses on a single bird species, the Carolina chickadee (Poecile carolinensis) and its diet in urban landscapes. Their conclusion: “…properties landscaped with nonnative plants function as populations sinks for insectivorous birds.” Thus, any gardener who happens to use introduced ornamental plants in their landscape is made to feel guilty for starving their insect-eating birds. (As an aside with my manuscript reviewer hat on – this statement has no business being in an abstract as it overextrapolates the research on one species to include ALL insectivorous birds.)

Carolina chickadee (Poecile carolinensis)

Black-capped chickadee (Poecile atricapillus)

The second article has a different focus. It reports the feeding of black-capped chickadees (Poecile atricapillus) on the larvae of a leaf-mining moth (Phyllonorycter emberizaepenella). While leaf miners are common food items for chickadees, the point of this article was to document the host of the leaf-miner – a nonnative and particularly invasive species of honeysuckle (Lonicera maackii).

Honeysuckle leaf miner (Phyllonorycter emberizaepenella)

Chickadees as a group are particularly adept at finding and consuming leaf miners, whose tunnels normally protect them from insectivorous birds. Chickadees move along branches,“examining leaves both above and below them; the chickadees sometimes scanned by hanging upside-down.” This makes it easier to find and extract leaf-miners, as the underside of the leaf is easier to tear open than the surface. And in fact this behavior is reflected among other species of chickadee and leaf-miner: “Similarly, in 15 years of study, Connor et al. (1999) never observed species other than Carolina chickadees (Poecile carolinensis) feeding on the larvae of the gracillarid Cameraria hamadryadella [oak leaf miner].” While these are not the same species of leaf miner studied in this paper, the point is that chickadees eat leaf-mining insects. And leaf-miners can obviously adapt to new food sources, including introduced plants. This is basic ecological science.

Oak leaf miner (Cameraria hamadryadella)

Neither Craves’s article (the second of these two articles) nor that by Connor et al. (cited within Craves’s article) are cited by Narango et al. (2018 – the first article), even though both are certainly pertinent to the topic. But they don’t fit the narrative – which is that introduced plants are not good food sources for the insects that chickadees eat. So they are left out of the discussion, which by default is now biased – not objective. Not science-based.

And I don’t have a good answer to the obvious question – which is why we continue to demonize noninvasive, introduced plants in the absence of a robust body of evidence supporting that view.