I have tried to grow a lot of plants in my greenhouses. They have ranged from orchids to vines, from seasonal vegetables to perennial fruit and I have found that there are certain plants that or either difficult, invasive or just plain ornery when grown in the greenhouse. They range from plants that cannot stand to be inside to invasive species that will take over everything if you let them.
I saw an online story last week that said you can grow corn in the greenhouse. Yes you can, but the results are disappointing. In the greenhouse there is no wind to shake the plant and pollinate the kernels, consequently the kernels on the plant are few and far between.
To get good results in the greenhouse you would have to shake the plant for an hour or two every day and set up a fan to blow pollen around. It is not impossible, but it is a pain.
Another plant not to grow in a greenhouse is a fuzzy Kiwi vine. First you need two vines for pollination and each should be planted in different pots. Unfortunately, Each Kiwi vine can grow up to 40 feet (about 12M) per season. That means they go back and forth in a small greenhouse where they can block out light for other plants or they grow through a window and need to be radically cut back in fall. In my 30-foot (About 9M) long greenhouse the vines snaked back and forth at the top of the greenhouse and did not produce fruit the first season.
Another vine that becomes a problem is passionfruit. Yes, the flowers are wonderful, but the vines not so. My passionfruit vine grew out through a greenhouse roof window and formed a huge dense mat on top of the glass that took up about half of the space available. When winter came, I had to cut the vine inside the greenhouse and pull the mat off the roof. After three seasons I’d had enough!
Growing through a top window was a favorite trick of the banana plants I grew. The stalks grew right through the 12-foot (3.7M) high window and set leaves and a spathe well above the greenhouse. I use banana leaves for cooking, but outside the greenhouse the leaves were shredded in the wind.
The spathe has both male and female flowers and eventually develops into bananas. The only problem I had was that this happened in late September. We get our first frost around the middle of October and there was no possible way to get the spathe back inside the greenhouse. I finally had to cut off maybe twelve hands of very unripe green bananas in order to close the window. After three seasons I decided the plant had to go and dug it out. Except, the next season, shoots came up and grew into banana plants. I dug them out and more shoots came. It took about five seasons to finally get rid of the plant.
I once grew a fig tree in a pot in the greenhouse. It sat in the same place for several years and I picked many pounds of figs off it. It grew and grew until it was pressing against the roof glass. It was just inside the door and made it difficult to enter. In addition, I thought it might burst through the glass and decided it needed to be moved. When I tried to move the pot, it had grown out through the bottom and into the soil and was impossible to move. I finally destroyed the pot, plant and floor of the greenhouse moving it. Its successors live outside the greenhouse in beds sheltered from the cold northwest winds, but they produce far fewer figs each season.