How to Grow Orchids in a Greenhouse

how to grow orchids in a greenhouse

Growing orchids in a greenhouse allows one to effectively regulate the conditions in which their plants live. All the equipment specific to raising orchids still applies in a greenhouse, but due to the enclosed settings, care of orchids can be easier. Of course, a few perks go along with it; yet, with a bit of patience, and some love for your specimens, good health and beauty can abound.

To grow orchids in a greenhouse, you'll need high humidity, warm temperatures, cooler nighttime temperatures (by 10-20 degrees Fahrenheit), and good air circulation. The amount of light needed varies by the variety (genus) of orchid; the most common--Phalaenopsis--orchids require low light.

Let's dive in!

how to grow orchids

How an orchid greenhouse is different

A greenhouse specially designed for orchids needs 5 things:

  1. Orchids need humid conditions.
  2. They prefer warm temperatures.
  3. They like fresh buoyant air.
  4. Their light needs are unique.
  5. And they benefit greatly from a drop in temperature at night.

By now you're probably wondering what all these particular preferences are about. In as little time as possible I'll try to explain the diversity and wonder orchids possess, and how to cater to them.

Light and temperature recommendations for orchid varieties

First let’s break-down orchids into a couple groups based on their light and temperature needs.

Usually terrestrial orchids (those that grow on the ground) require less light than their epiphytic (tree growing) cousins. Also, terrestrials can normally tolerate cooler temperatures than epiphytes.

Below is a table showing some common orchids and if they're low-light vs. high-light and cool temp vs. high temp. For light requirements, we've got 3 categories:

  • bright,
  • moderate, and
  • low.

Likewise, for temperature, orchids break down into 3 groups based on their temperature preference:

  • Cool- 60F-70F in the day and 50F-55F at night,
  • Intermediate- 70F-80F in the day and 55F-65F at night, and
  • Warm- 80F-90F in the day and 65F-70F at night.

Temperature and potting media (not soil!)

One thing that separates orchids from most houseplants is that most orchids grow without soil and prefer a temperature drop at night. Some orchids won't bloom if they don’t experience a drop in temperature at night. Another difference is that many orchids grow in trees where they get nutrients from rain instead of soil.

Since using potting soil is not preferred, a mixture of bark, perlite, peat moss, and in some cases, osmunda fiber and sphagnum moss is desirable. The amount of each material you use depends on what species of orchid you wish to grow, but a good rule of thumb is to use more bark or osmunda fiber for tree growing species and more peat moss or sphagnum moss for the ground growing species. Perlite is a good material to use in both instances to make certain the substrate drains well.

With any orchid, the max drop of temperature at night you should allow is 20 degrees Fahrenheit. But 10 degrees lower is usually all that's necessary to keep most orchids happy. Make sure there are no cool drafts at night though, as orchids hate them.

How much greenhouse space do you need?

Now that you know what orchids prefer in their greenhouse, let's discuss the greenhouse itself.

Consider the cost and size of a greenhouse when shopping for one. It's nice to be cost effective, but you need the greenhouse to be big enough for good air circulation, yet small enough to support humidity levels and good temperatures.

Orchids should be placed close to each other but not touching. Therefore, depending on how large the plants are and how many orchids you have, you should be able to figure how much space is a minimum for your needs.

For example, if you want to grow 20 Phalaenopsis orchids in your greenhouse, you could find that Phalaenopsis orchids average 12 inches wide, making a 20 square foot greenhouse the bare minimum. Keep in mind that doesn't account for walkways or for the bit of extra space needed to keep the plants from touching.

A simple greenhouse setup tip for orchids

To decrease the orchids' exposure to temperature fluctuations, you should keep them on benches so they aren't in contact with the ground.

If you have metal mesh benches, you can put the orchids on the benches & the trays of water under the benches to help with humidity--and kill two birds with one stone.

Speaking of stones, if you mulch the floor of the greenhouse with pebbles or bark, you'll reduce weeds (orchids don't like sharing pots) and insulate the ground better.

Controlling the environment inside the greenhouse

Once you've bought or built your greenhouse, you'll need to provide 4 things:

  1. a source of humidity,
  2. good air flow,
  3. sufficient light, and
  4. the right amount of water.

Humidity

Orchids like 60%-80% humidity.

I already suggested water trays for humidity, but if you don't want to clean out trays when they get green and gummy, you could mist the air with a fine spray at regular intervals throughout the day.

Don't use commercial misters as their spray isn't fine enough, and will leave standing water on the foliage and in the connections between leaf and stem. That water sitting on the orchid promotes stem rot and other issues, both hard to reverse.

You can easily check the humidity level in your greenhouse by installing a humidity gauge, this makes it a breeze to adjust, just add some warm water to your trays or mist the greenhouse with it when the gauge is reading a bit low.

Air flow

Air flow can be regulated in the summer with roll-up windows--which is a good idea, because of the fresh air too.

You may want to roll the windows down at night if the temps are going to be chilly or if a storm is expected to come through.

Some days you will need to rely on other means of air circulation though. Say it's too dry and hot out for your orchids. In that case, you can have small fans placed below the plants' level to keep the air moving in the greenhouse. Make sure the fans don't blow too hard and disturb the plants, since orchids are brittle and don't often recover from a bad fall.

If you have the extra surface area, spreading the orchids farther apart boosts air flow as well, but cuts the humidity levels. So be careful when rearranging the greenhouse.

There's no easy way to tell if the airflow is right, but generally if the air doesn't smell or feel stale or musty, it should be good.

Light, and how much

Orchids don't appreciate direct sunlight, so a shade cover can be helpful if the greenhouse isn't in a shaded area.

Most orchids like around 12 to 14 hours of light a day in the summer, and about 10  to 12 in the winter.

If you face the greenhouse in a southern direction, you may be able to get by in the summer fine without giving additional light to your plants. But in the winter, it's almost always necessary to put fluorescent bulbs or grow lights above them. The bulbs should be suspended roughly 6  to 8 inches above the leaves of the orchids.

You can purchase timers which turn the lights off at a specified time each night and turn them back on at a specified time in the morning, cutting down on the stress involved in trying to remember when to switch the lights on and off.

When your orchids are getting enough light their leaves should be a bright vibrant green, not yellowish or dark green.

watering orchids

Watering

Watering orchids is a little tricky. Giving them too much makes their roots rot and their leaves fall off. Giving them too little dries out their roots and makes their leaves fall off too. So if your orchid's leaves are falling off you have a problem on your hands.

As a rule, orchids need continually moist, but never sopping growth media.

Some orchids like to dry out completely in-between watering.

Enforcing a strict watering schedule helps make sure you don't water out of fear that they aren't getting enough. This schedule will have to be adjusted for the winter months and the summer months.

If you live in a humid climate, then in the summer the greenhouse will usually be a bit more humid and the orchids won't need as much water. You should still water as often as always to keep the substrate moist, but give a bit less water at each watering.

You shouldn't have to refill the trays or mist as often either (whichever you choose to do), if you live in a dry climate you may have to reverse the above scenario. It helps to experiment a little and find out what works the best for you.

Why ice cubes aren't 'cool'

One thing I want to clear up about watering orchids is the ice cube method.

Putting ice cubes in your orchid's pot is one of the worst things you can do. 

Remember I mentioned orchids hate cool drafts? Well placing something cold like an ice cube against an orchid's roots is pretty detrimental to its health.

An ice cube might work for the orchids you get from Walmart, if you're going to throw it out after they're done blooming. But for if you want to have your orchids around for the long haul, watering with ice cubes will be detrimental.

Although an ice cube is not the best idea, the amount of water it gives is usually perfect for a week for a single orchid--that's one reason using ice cubes is popular. So, you can measure a melted ice cube if you want to regulate water levels nicely. (It's about an eighth a cup of water, or two table spoons.)

Remember the actual amount of water will depend on the time of year and how dry or humid it is outside or in your house.

Growing media (remember--no soil!) and watering

Another thing you should take into account when developing a watering schedule is the type of material you've got your orchids potted in--remember: orchids don't grow well in regular soil.

Sphagnum moss, for example, dries out easily and doesn't absorb water well when it's dried out. So, you may need to water more frequently with less amounts of water.

Bark chips commonly dry out on top but stay wet at the bottom. So, when you're testing the water level test the bottom rather than the top.

Peat moss or other types of soil substrates dry from top to bottom as well, you only need to water again when the top two inches dries out.

Common orchid problems

OK, so let's suppose you've got your watering schedule down, but in the process of figuring it out, you watered one of your orchids too much, and it developed mildew or fungus on its growth medium. Or maybe you're having problems with thrips, or, worse case scenario, your plant has root rot.

How do you get rid of the problem?

Well, fortunately most of those problems have easy fixes.

Mold, mildew and fungus

Mildew and fungus are similar and can be eradicated with the same means.

To combat them when they're on the leaves, mix up 4 teaspoons of baking soda with a gallon of water, and add 2 teaspoons of insecticidal soap.

Dampen a wash cloth with the mixture and gently wipe the orchid's leaves.

Following this regimen twice a week the problem should go away.

If it doesn't, you can try a copper fungicide instead on the foliage, following any instructions the package gives.

When there's fungus on the surface of the soil, you'll likely have to repot the orchid, using a new pot and new potting media, and washing the roots of the plant with any of the above mixes.

Another alternative is to extract the plant from its media, bake the media in an oven at 450 degrees for half an hour, rinse the roots of the plant in fungicide or the above-mentioned baking soda and insecticidal soap mix, then repot it in its original materials.

Make sure to clean out the pot with fungicide, the baking soda mix, or diluted bleach (70% water to 30% bleach).

If the infection insists on the plant after taking action, you'll have to throw out infected pots and media, and submerge the orchid in full strength hydrogen peroxide to disinfect it, or consider disposing it.

Root rot

Root rot is a type of fungus or mold but is unique in its treatment. It's generally serious, and can take an orchid over a year to recover from.

The most common symptom is roots that are squishy, black, and fall off when a plant has it. Also, the stem can be blackish.

The best way to prevent root rot is to repot orchids every two years or so, and make certain they don't get too much water.

If your orchid gets root rot though, here's the remedy:

  1. Pull the plant out of its pot and remove all old media.
  2. Clean, cut or pull any roots and leaves that appear affected off of the plant, rinsing it thoroughly with water.
  3. If the rot is in the stem, the orchid will likely not recover.
  4. Once you've removed infected material you can apply fungicide to open areas to prevent mold and fungus.
  5. Plant the orchid in some sphagnum moss while it recovers, and be extra careful to watch its water intake, giving it plenty of fresh air.

Hopefully it will bounce back in a month or two if the infection wasn't bad.

Thrips

Thrips are tiny non-flying insects that eat an orchid's flowers and buds, sometimes living in the media for long periods of time.

 If you spot them skittering about on your plants, you'll need to take a couple of actions to get rid of them.

Thrips happen to be hard to deal with, but rotating between insecticidal soap, sticky tapes, and predatory mites can be a big help in winning the battle.

Insecticidal soap needs to be applied thoroughly on the plant and its growth media.

Cover its leaves top and underside, its stem and leaf connections, and if possible, its roots.

Tip the plant upside down to let excess liquid drain out of the leaf nodes.

Predatory mites should only be used in a greenhouse, as you won't want them running around the house.

Thrips also don't like to be flooded out, but if you choose to soak your orchid's pot, make certain you do so in a well-ventilated area so fungus problems don't surface and the plant can dry out again easily.

A common lookalike of thrips is another insect called a midge. They fly are tiny and can be gotten rid of in the same ways as thrips.

fertilizing orchids

Fertilizing orchids to boost blooming

Now, since we've got the problems out of the way, let's talk about how you can help orchids to bloom more.

Generally, when we think of helping a plant bloom we think of fertilizers. Orchids are no different. But they also can be teased into blooming with a few other methods.

Light is one of the factors determining when an orchid wants to bloom. So, you can boost the light intake by using artificial grow lights. An extra hour or 2 per day should help trigger an orchid into blooming. Using both grow lights as well as fertilizer can produce better results.

Phosphorous is the chemical that orchids need to bloom .But no matter how much you give them, if they aren't feeling good, they won't bloom. So, you can give them a balanced fertilizer (like 10-10-10 or 12-12-12) to keep them really happy.

Orchids don't require as much fertilizer as other plants, and often do better with their own rates of application.

A good way to fertilize orchids is to do half the recommended dose every month.

Once you've established growth, adding extra phosphorous and light will give your plants an obvious nudge in the right direction.

Caring for orchids during winter

For the well-being of your orchids you should only prompt them to bloom during the summer, and reserve winter as a rest period. Below are a few tips for caring for orchids during winter.

First, determining if wintering orchids outside is even a possibility requires you to find out what zone you live in. Zones are areas split by the average winter low in ten-degree increments. Zone 10 for example only drops to 30 degrees in the winter, while zone 9  drops to 20 degrees Fahrenheit. If you search with your area code, you can find what zone you live in.

Wintering orchids outdoors is possible in zones 10 through 13. That assumes you get enough sun to keep the inside warm enough or provide additional heat.

In cooler zones, it's best to move the orchids inside for the winter.

Deciding whether to winter orchids in the greenhouse is mainly up to your budget and the size of your greenhouse. Smaller greenhouses are easier and cost less to heat. If your greenhouse is large, you might section off one corner of the greenhouse to fit all the plants and reduce heating needs.

Insulating the greenhouse helps keep the heat inside, but can shut out vital light. In that case, artificial lights might be needed.

Insulation can make the air stale too. So, small fans and/or vents can keep the air fresh.

Related Questions

How much light do orchids need indoors?

Orchids need 12 to 14 hours during the summer, and 10 to 12 during winter. Use artificial grow lights when the days aren't long enough, or you don't have a well-lighted spot for them. Orchids need the same amount of light whether they're indoors or outdoors

How long do orchids bloom indoors?

On average orchids bloom a little over a month. However, with proper care, flowers can last several months at a time. The range in bloom duration varies from a few weeks to two years, depending on the species of orchid.

How long does it take for an orchid to rebloom?

Generally, an orchid will bloom once a year. Some species bloom twice, and if you employ the methods shared above in this article, you may just tease one into blooming over and over continually.

About the author

Greg Volente

Greg Volente holds a Naturalist Certificate from the Morton Arboretum, worked for The Nature Conservancy leading environmental education programs and doing natural areas restoration, and worked in the soil science research & testing lab at Michigan State University. Besides gardening, he's an avid wildflower enthusiast, and loves botanizing, hiking, and backpacking.