Another question I’m asked way more than I’d anticipated is how I’ll prevent ‘intruders’ such as bugs, birds, and various rodents from taking up residence inside the greenhouse and then inside the house. These questions used to confuse me because I wondered why anyone would think my greenhouse-protected home would be more vulnerable to critters than a standalone home. Frankly, I thought the questions rather knee-jerk and silly. But the more I thought about it, the more I realized that I was the one with the knee-jerk response. Early in the process I had only an intellectual understanding of the greenhouse’s inter-relationship with the house and its impact to how I would live in the spaces. Only after the design was complete for the house, the greenhouse structure, and the space within the greenhouse was I able to visualize moving through the spaces and how the greenhouse will change daily life within the house.

Once I could close my eyes and dream about performing ordinary life tasks around the house and greenhouse, then I understood the greenhouse’s shelter on an emotional level, not just an intellectual level. My reasoning shifted from ‘rodents, birds, and bugs do not interrupt my 3-4 months of outdoor living now’ to ‘how do I stop rodents, birds, and bugs from interrupting my ‘outdoor’ living once I’ve provided a climate-controlled and sheltered home for them.’¹ Inherent in this question is recognition that I can not prevent these intruders getting into the greenhouse; my goal is to minimize their stay and destruction while there.

The main critters to manage are mosquitoes, birds, and rodents. My intent is to use only natural control methods and never chemical means. Therefore, the method to deal with each type of critter varies by the conditions that minimize attracting them and encourage the conditions that repel or kill them.

Rodents

Rodents may be attracted to the greenhouse because inside will be warm and dry, provide a water source and ready food sources, and will be safe from predators. The rodents prevalent in this area include chipmunks, rats, mice, and shrews. Natural predators prevalent in this area include owls, eagles, and coyotes. Having lived on my property for almost two years I’ve had plenty of opportunity to monitor their presence. While I have, occasionally, seen a rat or chipmunk, there has been no evidence of them inside the trailer, garbage can (covered metal), cabins, or compost bin (covered). I take this as an indication that predators are keeping their numbers under control, and there are sufficient safer food and housing sources that they don’t need to risk invading human territory, or risk exposure to predators by crossing open ground to enter or exit.

Clearly it is best to prevent rodent entry to the greenhouse in the first place by sealing any gaps. We’ll seal the space between the greenhouse and the ground by attaching hardware cloth to the bottom of the greenhouse wall with the other end buried in the ground. However, mice can squeeze through amazingly small gaps – as small as a #2 pencil, so when the doors are closed, the most likely entry will be the small gap where the sliding doors meet and between the sliding doors and the wall. Even though the plan is to keep the doors closed except when necessary, the doors may be open for an extended time when moving materials in or out and possibly to provide air movement if the ground-to-air heat exchange tubes do not provide sufficient air flow. To discourage entry through the double-doors I’ll keep the ground clear for several feet outside that end of the greenhouse where rodents would be exposed to predators while crossing.

With all of these barriers, I do not expect rodents to become an issue inside the greenhouse. That said, my cat will be the first line of defense against any rodent that does get into the greenhouse and peanut butter baited traps can be the second line of defense.

Birds

I expect that birds may accidentally enter the greenhouse either through the ridge vents or the double-doors and then not be able to find their way out again as opposed to intending to move in permanently like rodents. Like the local rodents, however, my property appears to provide sufficient natural resources that birds are not forced to risk entering human or cat-controlled territory.

Local ‘pest’ birds include robins, starlings, sparrows, and crows. Given the wealth of food and shelter outside the greenhouse, the most likely attraction will be water during the dry latter summer months. Summer is also the time of year the doors are most likely to be open and the ridge vents will be open to exhaust hot air. For any bird that enters the greenhouse that wants to exit, the convection-fueled rising air should provide direction through the ridge windows that run the entire length of the greenhouse on both sides of the ridge beam – an opening approximately 4’ wide by 60’long.

The birds that have bothered my vegetable garden are opportunists who may be deterred by minimal effort. One of the easiest and least expensive is to string shiny party streamers along the trusses. Or, sprinkling baking soda on beams or trusses where they perch. Or, to place a predator decoy, such as an owl, on the greenhouse roof. An owl decoy has worked very well to keep herons from my koi ponds at a previous house. Ultimately, I think I will not need to pro-actively include any structural bird barriers such as screens. I may, however, implement deterrents in the future based on the method and reason for the bird’s entry.

Bugs

I accept that insects of all kinds will get into the greenhouse but insect control is where things get a bit tricky because I want to attract beneficial insects into the greenhouse while minimizing the offensive insects. Pollinators cross a wide spectrum from non-annoying (ex: mason bees, ladybugs, and butterflies) to annoying and potentially harmful (ex: wasps and mosquitoes). Each insect has environmental conditions that attract or repel them that I’ll leverage in the garden designs.

The plan for the greenhouse’s garden space is for, primarily, ornamental plantings on the east side of the house with some herbs and berries mixed in. Then, primarily, food plantings on the west side of the house with some pollinator-attracting flowers mixed in. I’ll try to select plants that do not require pollination but air movement will provide some cross-pollination. Still, I will design the gardens to attract and support pollinating insects and will actively introduce beneficial insects.

Beneficial Insects

Two beneficial insects that I will not only construct an environment to support them but will also specifically introduce into the greenhouse are mason bees and ladybugs.
Mason bees need access to a nest, flowers for food, and a mud source. I’ll make a few nests from blocks of non-treated scrap wood that will be hung throughout the greenhouse. They also need a source of mud to use in their nests so I’ll provide a ‘right-sized’ dish of mud on each end of the greenhouse. Mason bees prefer tube-shaped or irregular shaped flowers and are attracted to yellow, blue, purple, and white which are also my favorites. Selecting plants that bloom at different times will provide a succession of food sources to encourage the bees to stay in the greenhouse rather than looking for alternate food outside.

Ladybugs There are many types of ladybugs and most, but not all, are beneficial as both pollinators and because they eat pest insects, such as aphids and spider mites, which are common in my area. Ladybugs also eat some of the same flowers I’ll grow for the mason bees plus flowers that attract butterflies (ex: butterfly weed) and culinary herbs that I’ll grow for my own use such as cilantro, parsley, and dill. They also need a water source. The water in the ponds and lap pool will always be moving so that there is regular movement through the filters and to prevent mosquitoes breeding. I’ll probably provide a shallow, saucer-sized puddle at the edge of each pond that will be enough for the ladybugs and I can monitor for mosquito larvae.

Pests

Mosquitoes are a nuisance in every area of the United States and the Pacific Northwest is no exception. I hope to be able to have the house doors and windows open to the greenhouse throughout most of the year. This will not be possible, however, unless I can control mosquitoes inside the greenhouse. The mosquito control plan will use a few techniques targeted at both the larvae and adults.

Many species of mosquito breed in standing water so one of the most effective ways to control mosquitoes is to prevent standing water. The two possible sources of standing water in the greenhouse are puddles from irrigation, as well as, the ponds and lap pool. To prevent puddles, the plan is to use only drip irrigation and soaker hoses on raised beds. The low spot will be the paths between the raised bed which will have a thick layer of wood chips. Therefore, even if I over water the plants that runs down to the paths, there should not be open puddles in the paths.

Mosquito should not be able to breed on either the lap pool or regeneration ponds because the water will always be moving to circulate through the filters. Therefore, there shouldn’t be sufficient surface tension to support larvae growth. In addition, there are a few mosquito predators native to my area, such as frogs and dragon flies, that I expect to naturally move into the greenhouse. While I’m not currently planning to have fish in either pond, there is the potential to add them in the future to eat mosquito larvae if needed.

Finally, “[b]ecause mosquitoes are not strong fliers, it’s also easy to suck them onto a screen or into a separate trap using a fan. Mosquitoes caught using a fan die from dehydration.”²

Conclusion

Ultimately I can only do the best planning I can. Even if these techniques don’t provide a fully pest-free environment they should allow the greenhouse environment to be substantially better than outside. That said, each technique will be tested once I move in and there are additional measures that can be implemented if needed. Stay tuned as I’ll post the results of these pest-control measures over each season.

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¹This post focuses on birds, insects, and rodents as annoyances to living inside the greenhouse as opposed to their impact on the plants in the greenhouse. I’ll have separate posts about controlling greenhouse garden pests when I begin the detailed garden design.
²https://www.thoughtco.com/how-to-kill-mosquitoes-4160066

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