Where I live, the winters are long, cold, wet and horrid—they’re enough to make me long for the brilliant fiesta of summer way before the last cold snap is in sight. There isn’t much you can do to cure the winter blues when the ground is frozen, unless you’ve got a greenhouse where you can hole up until the grass starts to emerge from the snow. Tomatoes and the typical garden fare are rewarding and practical in the greenhouse, but there’s something extra special about turning that space into a slice of tropical paradise while the rest of the world is still blanketed with ice and snow.
Setting up a tropical greenhouse
Contrary to popular belief, tropicals don’t need blazing hot and crushingly humid conditions in order to thrive. In fact, these plants generally do best between 60 and 70 degrees Fahrenheit (15 to 21 degrees Celsius), with 70 to 90 percent relative humidity. It may be difficult to get so much humidity going in the winter, but do the best you can: employ misters, water the ground and sit plants on trays of rocks containing water if necessary. The other thing you’ll need for success with tropicals in the greenhouse is supplemental light.
You see, winter sun is different from summer sun. Not only does it stay visible for less of the day and is more frequently hidden by clouds, the rays are less intense because they’re coming in at a different angle than during summer. The Earth is actually tilted away from the Sun during whatever part of the year we perceive as the winter (it’s the opposite time of year for the Southern Hemisphere). Because of this, your greenhouse needs supplemental lighting if you’re going to use it through the winter for any plants with high lighting requirements.
If you have a very large greenhouse, you may have to add several expensive waterproof fixtures to get the lighting just right. Luckily, the average backyard greenhouse can usually get away with relatively inexpensive fluorescent fixtures fitted with high output, broad-spectrum tubes. I typically use 2900 lumen bulbs, both because they’re affordable and because they put out a reasonable amount of light.
The thing with the high-output monster lights from the catalogs is that they’re really designed to hang 10 or 20 feet off the ground—if you’ve not got that kind of space, you may over-light your plants (this is a real thing) and kill them. Light meters are available to help you decide how much lighting you really need, but if you’re running a greenhouse less than 20 feet long and eight feet tall, fluorescents are the way to go.
Moving into the jungle
You’ve got your greenhouse ready, the lights are up and the heater’s in place—it’s time to get started! First of all, and I can’t stress this enough, plants don’t like change. None of them. I don’t care if their scientific name is Asteraceae change-a-lottus, they’re not going to handle a move with grace and style. If you’re moving your jungle from your home to the greenhouse, it’s not a huge challenge to set your greenhouse to the same conditions your plants have indoors. Just take some readings near your plants and tweak your greenhouse until you’ve got your equipment replicating your home’s temperature and humidity.
But what about all that stuff I said above about the temps and humidity that your plants need in a greenhouse? I can hear you through the computer, I think I’ve told you that before. Anyway, that’s where your skills as a greenhouse operator are going to come in handy. It takes time for your plants to acclimate to different weather patterns, but in the greenhouse, you’re in control of everything. Move them in under conditions they can manage, give them a few days or a week to settle in and watch for problems.
If everybody’s reasonably happy, start increasing the temperature, the humidity or both, but do it slowly. A degree or two every few days and five percent humidity at a time is all it takes—go slow because your plants accept change slowly and in small increments. If you make a change and suddenly you see a lot of drying, wilting, yellowing or general fit-throwing, back off and try again in a few days. The same applies if you’re going to move the plants back indoors at some point. Work them down to indoor conditions slowly.
Your plants’ solar exposure may be dramatically different between indoor settings and the greenhouse. Shade cloths can help if your greenhouse isn’t frosted, but it’s tricky at very best to determine how much is needed without exact light readings. If you’ve got a good light meter, though, starting with artificial light only (mimicking the conditions in your home) will help prevent sunburns. As with your temperature and humidity tweaks, remove the shade cloth for a little bit each day until your plants can tolerate the sun.
Leaves grown under lower indoor lighting conditions are very sensitive to the sun because they’re designed to capture all the available light possible. Outdoor plants know the world is their oyster and often have much less efficient leaves that protect themselves from sun exposure. Your plants can grow both kinds of leaves, if you give them time to adjust. Be aware that outdoor lighting conditions may vary from your greenhouse conditions, so an adjustment period is recommended if your plan is to move your tropicals outdoors for the summer.
Stocking your tropical paradise
We’ve discussed how to set up your greenhouse, how to move your plants in and out and in and out again, but we’ve not gotten to the good part yet: the plants! There are so many gorgeous tropical plants that I can hardly list them all, but I will give you a little rundown of some of my favorites to help you get started.
Orchids - Always at the top of my list, orchids are easy to care for once you understand their needs. Most common, easy species like the Phalaenopsis grow in the wild in branch crotches under a great deal of shade, so they’ll need bigger plants to protect them from intense light or a lower-output lighting setup of their own. The thing they don’t need is potting soil—bark mix or sphagnum moss will keep their root systems wet enough to thrive while giving them plenty of air.
Bananas – There are so many varieties of small, ornamental bananas that it’s impossible to list them all, but know that no matter what you’re looking for in a banana, it’s out there. Variegated foliage, foliage with splashes of red (also known as the blood banana), pink bananas, black bananas—you name it. You’ll have to get named varieties from a specialty grower, but they’re super easy to get going once you find what you want.
Birds of Paradise – This flashy cousin of the banana is an excellent greenhouse companion for them. They’ll need big containers and lots of patience to bring to bloom, so start with mature specimens until you’re very familiar with the family. Treat them just like bananas and provide excellent drainage for best results.
Cycads and Palms – Dwarf varieties are the name of the game, but if you’re going to build a knock-out get away, leave these guys at Home Depot unless you’ve got a lot of space to fill or need something to filter light. There’s nothing wrong with cycads and palms, but they’re all green with no big payout… when space is limited, throw them out.
Citrus – Limes and lemons may seem like an odd combination in a tropical greenhouse, but in fact they’re quite at home there. Again, look for dwarfs unless you’ve got the space for a monster tree that may reach 30 feet or more in its lifetime. Walking into a greenhouse with ripening citrus is sort of like walking face-first into a sunny spray of dishwashing soap—it’s refreshing and beautiful and will probably make your eyes water a little bit.
Passion Flowers – Another food-bearing plant native to many areas of the U.S., the passion flower is a gorgeous subtropical vine that will do just fine under tropical conditions. Their blooms are unsurpassed by anything on this planet, with many hybrids sporting unusual fringe, decorative tassels and bold colors. If you’re very lucky and learn to hand pollinate these beauties, you can even get them to bear sweet passion fruits. Leave plenty of room for passion flowers and hang a trellis, they’re going to need it as they spread out.
Poinsettia – Just because the holidays are over doesn’t mean that these bright, beautiful Euphorbias are done—in fact, they’re long-lived perennials that will rebloom consistently with proper care and grooming. I happen to have four of the white and red variegated types, and I can’t think of anything I’d rather find while wandering in paradise. They prefer to be on the dry side, so keep them away from misters and wick-type watering systems—root rot is a real problem for poinsettias.