• Emily

Let in the Light

Updated: Apr 8, 2021


peppers sprouting in the growing dome

If you haven't already, now is the time to clean the transparent walls and ceiling of your greenhouse. Whether you have a growing dome like ours (from Growing Spaces), or a rectangular greenhouse, hoop house, etc., the effectiveness of your structure is largely determined by how much light it allows through to your plants.

Every growing season, dust, moisture residue, and plant debris collect on the walls and ceiling of our growing dome. While some of it is caused when overspray from watering splatters the glazing, a large part of the residue is caused by the inherently humid environment. As plants respire and moisture from the water tank evaporates into the dome's atmosphere, droplets collect on the walls and ceiling. This moisture traps dust; if it builds up in excess, it can develop mold or mildew.

This time of year, new seedlings need as much light as possible to get a strong start. We wait to clean the glazing until the weather is consistently warm and temperatures in the dome are starting to climb. Now is the perfect time to clean the greenhouse and let in the spring sunshine.

shallots and Swiss chard growing in the greenhouse

What surfaces should be cleaned?

When dome-cleaning day rolls around, Kindra and I usually focus on the glazing (the clear polycarbonate from which the walls and ceiling of the dome are made), and any metal, plastic, or wood surfaces that are looking grimy. In our dome, metal strips attached to the glazing (to shed condensation) tend to accumulate a fair amount of dirt and plant debris during the growing season. These are wiped away and any remaining dead leaves are sent to the compost. The wood of our pergola structure and the beam over the water tank benefit from being reoiled once each year to withstand the constant moisture of the greenhouse atmosphere. The plastic surfaces of the tank liner and ventilation fans benefit from a scrubbing as well.

What cleaner should I use?

We are very cautious about introducing any chemicals into the growing dome. In that closed environment, we use as few traditional cleaning products as possible. Fortunately, the polycarbonate glazing cleans up easily, and a water/vinegar solution (or just water) works well. We have found that the very best tool for reaching all the corners of the greenhouse panels is an extendable window cleaning tool with a microfiber scrubber that fits over the end. The plush scrubber can be easily rinsed between panels and is able to clean even tight corners effectively.

a plush window scrubber on extendable pole is a perfect tool for cleaning the greenhouse glazing

For the water tank, tank liner, and ventilation fans, we use water or a water/vinegar solution. Because the residue caused by humidity isn't greasy, it doesn't require soap to break it down.

Wooden structures like our pergola or the beam across the tank will suffer from the constant humidity if they aren't protected with some kind of oil. As with cleaners, we don't want to introduce anything to the dome that isn't biodegradable and food safe. Food-grade mineral oil does an excellent job of keeping the wooden structures in good condition year after year.

Other Cleanup:

If you didn't clean out dead foliage and trim back plants in your winter greenhouse, now is a great time to clear them away. Your new plants will need as much light and airflow as possible; leaves and stems that are decaying or lying on the soil's surface are vectors for pests and mildew.

Speaking of pests, spring is often when you will discover if pill bugs and slugs multiplied during the cool, wet winter. Natural predators like frogs can be a real asset in the dome, but sometimes it's necessary to take other steps. Even before new plants are in the ground, we apply a sprinkling of Sluggo (a natural product containing iron phosphate that kills slugs and breaks down into the soil). By destroying a few generations of pests before plants are in the ground, you get a leg-up on the competition for your vegetables.

lettuce plants growing in the greenhouse

With spring in full swing, getting the greenhouse ready for this year is top priority. It is well worth the time it takes to tidy the beds, maintain the structure, and let in the light for the season ahead.

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