Hearing a tiny, sharp pop in a greenhouse on a gloomy, wind-battered morning brings satisfaction. There is nothing earth-shattering here. There is a letting go going on. Almost indignantly, a seed pod finally gave way after weeks of trapped heat dried it out. The container threw its contents across the bench. It was shocking for the first time. A greenhouse can provide one of the more subdued thrills after that.
Greenhouses are typically associated with meticulous, thoughtful growth. The delicate things moved forward. Tender cuts wrapped in fleece. There is truth in that; any seasoned greenhouse gardener will tell you that caring for plants that would not otherwise thrive is a peaceful experience. There is, however, more to it than that. Some plants react more aggressively when exposed to that warm, humid, nutrient-rich environment. It’s too early for them to bloom. As a result, they spread faster than expected. Some of them literally engulf themselves.
In a violent, compressed way, the pop’s mechanism is sophisticated. During the drying process, seed pods from plants like Oxalis, the wood sorrel, develop internal tension. Think of it as a thin skin covering a coiled spring. In the correct circumstances, the skin splits and the pod contracts so rapidly that the seeds are thrown outward, sometimes two or three meters away, with a loud enough sound to make you look up. Even the slightest finger brush triggers the pods of touch-me-nots, Impatiens capensis. Ruellia, also known as hairy-flower wild petunia, is similar. There is nothing kind about these plants. At some point in their evolutionary history, these plants decided that patience was unnecessary.
A greenhouse accelerates all of this. In a warm environment, pods dry more quickly. Because they are protected from wind and rain, pods can reach their full tension without being prematurely disrupted. A botanical trebuchet is set up, and the plants use it to their advantage. Many indoor gardeners are unaware of what to expect until seeds appear in nearby pots, shelf corners, or along the edges of the tiled floor.
One type of explosion is silent, but may become more dramatic over time. A greenhouse is a perfect place for lantanas, which are commonly referred to as weeds in warmer climates. It spreads relentlessly with a joyful relentlessness when given a small amount of space, constant moisture, and warmth. Similarly, nasturtiums grow so rapidly that you can follow their progress week by week. In waves of orange and yellow, it cascades off benches with an almost competitive speed. The theatrical excess of canna lilies is well known. Their large tropical leaves unfold dramatically in hot, humid weather, and soon they take over any available space. There is almost an artificial look to their flowers because they are so vibrant.
Wave petunias seem to completely misunderstand the concept of moderation. In a warm, safe environment, they bloom thousands of flowers and spread outward in all directions, covering benches and extending to the ground. In fact, they seem to be performing more than they are growing, putting on the most lavish show possible because the circumstances finally allow it. In a single winter under glass, Salvia curviflora, a Mexican sage, doubles in size or even triples in size, erupting in an incredible purple cascade. There is no nuance to it. There is no effort put into being.
In fact, greenhouses merely eliminate the barriers that typically prevent these tendencies from developing. A dry spell stalls progress, a strong wind damages fragile pods, and a cold snap slows growth. Under glass, those brakes are raised. Because the warmth signals that spring is already here, spring flowering bulbs such as tulips, daffodils, and hyacinths bloom weeks before their outdoor counterparts. Larkspur produces color spikes more quickly and intensely when grown in a polytunnel or greenhouse. In response, brugmansia, the angel’s trumpet, blooms with an almost urgent extravagance, as if it had been waiting for this degree of warmth and safety its entire life.
Watching this develop over a season is almost philosophical. Often, greenhouses are portrayed as a haven for delicate items. That’s all there is to it. For the right plants, it can also be a place where the limitations don’t apply, allowing them to fully express themselves. Those who were explosive, aggressive bloomers, and early forcers didn’t hold back out of preference. They had to hold back due to the circumstances outside.
That’s either reassuring or a little scary, depending on your perspective. It’s most likely both. It’s impossible not to feel a tiny sense of pride the next time something pops among the shelves and seeds scatter across the floor, as if the greenhouse itself had something to do with it. In a sense, it did.