Keeping a long-term monoculture greenhouse experiment alive and working over 2-3 years is not as easy as one could think. In the first year 2023 we already encountered some serious issues, including four near-disasters involving frost, fire, water and hail. This year, 2024, the obstacles are quite different as you can read in this report about the first half of the year.

Introduction

We are in the second year of our greenhouse experiment with up to 400 pots. Our aim is to gain a better understanding of the chemical, physical and biological processes in the soil when rock dust is added to induce enhanced weathering as a means of combating climate change.

This whole experiment is a lot of work, especially the tedious sampling and measuring every 4 weeks. Additionally we have to fight various obstacles along the way. In 2024, it seems that biology in particular has decided to give us a hard time: we've had numerous pest attacks that we've had to fight off to save our precious grass pots - while making sure we don't sacrifice or contaminate our experiments in the process. Plus some practical problems like in the first year.

Here is a report from our newest team member, Anke Anna Stöckel, about the attacks on our experiment.

A new job

*Something I would never have dreamt of: Spreading lacewing larvae on a pot of grass with a salt shaker 😀*

As I embarked on my new role in the greenhouse, filled with anticipation for scientific exploration, I was eager to uncover new connections, dive into data analysis, and expand our knowledge.

Yet, as I delved deeper into this unprecedented experiment, I quickly learned that surprises awaited around every corner. Each day now brings fresh and occasionally unexpected challenges - some involving encounters with previously unknown creatures.

I've come to appreciate that being a 'scientific problem solver' is just as important as being a traditional researcher. Although I sometimes long for the orderliness of a tidy desk, the dynamic environment of the greenhouse fascinates me and offers an exciting lack of routine that keeps me on my toes - and happy with my new job every day.

Several waves of pests

Here’s a (non-chronological) list of the many challenges we’ve faced. Initially, some of these issues might have seemed more appropriate for a "My Beautiful Garden" section rather than a scientific experiment.

It all started when, almost overnight, the grass in many pots began to look strange and then died in many more pots over the next few days. Fortunately, we have skilled gardeners working in the greenhouse below ours, and we asked for their help. The diagnosis was grim: mildew, thrips, and aphids—a veritable zoo! We had to act quickly and carefully to avoid contaminating our pots with unwanted substances. After much discussion and research, we developed a plan for each issue.

Powdery Mildew

Powdery mildew (Erysiphaceae) is a fungal infestation that is also known as ‘fair weather fungus’. It can be recognised by a whitish, flour-like coating on particularly young parts of the plant, mainly on the upper side of the leaves.

Due to the feared rapid spread in our greenhouse, all the grass was cut from the pots at lightning speed. We then opted for a treatment with raw milk twice a week. This involves diluting raw milk, which was collected fresh from the milk filling station on the same day, 1:8 with irrigation water. Each of the 349 pots received five sprays for several weeks. The treatment, effective due to the bacteria in raw milk, was meticulously documented to quantify the input of calcium, magnesium, iron, potassium, and sodium. After six weeks, all the pots seemed completely free of mildew. As a German proverb says: “Die Milch macht’s!” - It's the milk that does it!

Another natural treatment method would have been natron, but here the amount of hydrogen carbonate administered is quite high, so we have decided against it.

Thrips

Thrips are pests that mainly occur on houseplants. When infested, silver suction marks appear on the upper side of the leaves and the leaves appear transparent. This is what happened to around 50% of our pots within a very short time.

To get rid of the pests, we first decided to use lacewing larvae (Chrysopidae) as beneficials, as they prey on both thrips and aphids, of which we also found some in the greenhouse. Applying them proved to be difficult as some of the larvae were still so tiny that we had to use a saltshaker to distribute them evenly and some of the larvae that had already developed were very hungry and even bit us (ouch!!).

After a few days, however, most larvae had disappeared, so we moved to plan B: predatory mites.

Two types were required, as thrips should be controlled at as many stages as possible. Some of the mites were in pouches (Neoseiulus californicus), which were gradually placed from pot to pot and some of the mites crawled out each time. Another species has been placed in heaps in each pot and is (hopefully!) spreading independently (Hypoaspis).

In order to monitor the infestation, sticky blue tags were attached to some of the pots. Some of them had tiny thrips on them at first, but now we hardly see any more.

We have also discovered a few specimens of black flies, also known as fungus gnats, on the control panels. Fortunately, one of our beneficial mite species is also a natural enemy of fungus gnat larvae and we hope to get this problem under control. Killing two birds with one stone, so to speak :-)

Aphids

Aphids (Aphidoidea) are a common nuisance for gardeners. These tiny pests are known and disliked by many, whether they infest our gardens or occasionally make their way into our homes.

Initially, fortune seemed on our side. The aphids disappeared naturally as the grass either wilted or was cleared for new seeds. However, with the resurgence of healthy grass, the aphids returned in formidable numbers.

To combat this ongoing issue, we're turning to a new ally: ladybug larvae (Adalia). Known for their hearty appetite for aphids, we eagerly await their deployment in our greenhouse (and hoping they're not as ravenous as those lacewing larvae). With fingers crossed, we trust these little ladybug larvae will swoop in, chow down on aphids, and bring back the balance to our ecosystem.

Dying grass, overflowing pots and pCO2 computers as victims

The deterioration of grass in many of our pots was frustrating, not only for those who appreciate a lush lawn, but it also presented a major challenge to our ongoing experiment. Grass plays a crucial role by absorbing CO2 from the air through photosynthesis and enriching the soil. Its decline can be attributed partly to the aforementioned pests and partly to clogged root fleece in some pots. Despite its advanced design, the fleece became densely packed with clay particles smaller than 2 μm, transforming the pots into small ponds rather than verdant patches of grass.

At one point, the pots were so waterlogged that we even had pond plants like the floating liverwort (Ricciocarpos natans) thriving in them. We removed the vegetation, reduced irrigation, and sometimes disconnected it for days, trying to save what we could to keep the grass from turning into a swamp and our little green friends alive.

Water also accumulated on the lids of the leachate tanks, bringing with it plenty of iron deposits. We tried various remedies here as well: installing spacers between pots, drilling or cutting plastic needles into the fleece, but alas, 16 pots didn’t make it.

The surviving pots received emergency care. They were reseeded with grass and covered with foil for 3-5 days. We also carefully removed moss with forks to give new grass blades a fighting chance. The extracted grass was dried, sifted, and the soil from the roots returned to the pots.

In addition, overflowing pots and dying computers became our new norm for table 1. Due to swelling clay particles, the soil expanded more than the pots could handle, causing a lot of soil to spill onto table 1.

Moreover, the high clay content reduced the flow rate, causing water to drip from every conceivable crack, which led to the flooding of some pCO2 computers. Sadly, this resulted in irreversible damage to several of them. We replaced them and collected the spilled soil which was weighed for future calculations. Unfortunately, the pCO2 sensors in three pots shorted out and future measurements in these pots will not be possible☹️.

As if all that wasn't enough our cistern developed a stench in May, likely thanks to the massive pollen influx this spring. Depending on who you ask, it either smelled metallic, foul, or a delightful combination of both. The pollen may have disappeared, but the strange smell lingers. To get to the bottom of this olfactory mystery, we'll be sampling water at FAU — one sample from May and two from June for comparison. The samples will be analyzed for the entire periodic table to pinpoint the cause of the funk.

And even more fauna and flora

Apart from pests we are seeing other living things in our greenhouse cosmos all the time.

Here are a few of them:

Wolf’s milk (Lycogala epidendrum) on the soil. We found them earlier this year when a lot of pots were reseeded due to grass that died because of the missing light in winter. These heavy metal accumulators are left in the pots to avoid falsifying the experiment.

Algae (unknown species) in the soil pots and the water control pots and our drinking water tank. These problems were easy to solve: Control pots were cleaned, algae on pots were carefully removed, drinking water tanks were provided with new silver ion meshes.

Snails: Only small specimens. They felt particularly at home in the flooded pots.

Spiders (domestic house spiders and cosmopolitan cellar spiders): forming a natural part of our greenhouse ecosystem.

Ants: Thankfully, only at the bottom beneath the gardening tables, not in the pots.

Earthworms: (Lumbricus terrestris): beneficial creatures live in our pots, loosening the soil and improving its structure, and enhancing its fertility.

Our journey through these unexpected obstacles continues, filled with learning and adaptation at every turn.

Stay tuned for more exciting updates from our greenhouse adventures as we tackle whatever comes next!

Greenhouse Adventures: A journey through unexpected obstacles (Part 2)