12/19/2022 | Agriculture and Farming | 8 MINUTE READ

How to Grow Poinsettias in a Greenhouse

poinsettias

If you have a greenhouse and are searching for the perfect plant to grow during the holidays, poinsettias are a favorite at this time of the year. Along with the beautiful colors, many growers opt for poinsettias during the winter because of the high profits they bring in and the ability for these flowers to flourish despite the cold temperatures. Keep in mind that poinsettias alone make up a $250 million industry.

While most plants and crops that you can profit from grow best during the spring or summer months, growing poinsettias during the winter allows you to continue bringing in greenhouse income. Even though poinsettias are able to thrive during the winter, there are some best practices that you should adhere to when tending to these flowers. This guide covers everything you need to understand about growing poinsettias in your greenhouse.

poinsettias growing

Greenhouse Poinsettias Best Practices

The following takes a look at some of the best practices that can help you grow greenhouse poinsettias.

Why pH is Important in Poinsettia Greenhouses

When you’re attempting to grow poinsettias in greenhouses, the pH levels are highly important. If you acidify the irrigation water for poinsettias, the crops can grow at a faster rate. Keep in mind that any water measurements with a pH reading below 7.0 are acidic. All measurements above 7.0 are alkaline.

When you want to acidify irrigation water, you should use nitric acid or sulfuric acid. While phosphoric acid is considerably safer to handle, it’s also much more damaging to the health of the leaf.

pH testing

Less Daylight Triggers Poinsettia’s Beautiful Colors

The majority of flowers bloom during the spring and summer months. While some flowers also do well during the fall season, poinsettias are one of the only types of flowers to grow well during the winter. When these flowers bloom, a pigmentation change takes place. This discoloration only occurs once sunlight drops to around 10-12 hours per day, which is during the winter.

At this time of the year, the flowers can display many more shades and hues that match Christmas tones. White, green, and red are some of the most common colors, which gives them their popularity during the holiday season. Keep in mind that poinsettias don’t grow well when kept below 50 degrees Fahrenheit, which is why your greenhouse will need to be properly heated.

Grow Beyond Winter: Light Deprivation

As touched upon previously, light deprivation can be good for poinsettias, which makes it feasible for you to grow them all throughout the year. If you plant these flowers in a light deprivation warehouse, you’ll be able to protect them from light exposure when they don’t need it.

With this technique, you can simulate the short day-length that poinsettias require to display their vibrant colors. The main benefit of growing these crops during the summer is that there should be much less overhead since heating and energy consumption will be lower.

How to Grow Poinsettias in a Greenhouse

Growing poinsettias in a greenhouse can be accomplished in seven simple steps, which include everything from preparing a container to keeping the plant covered.

greenhouses

Prepare a Container

The container you use should drain well. Make sure that you fill this container with standard potting mix. Some organic matter should be positioned on top of the potting mix, which you can do with a hand trowel. The organic matter you use provides plants with the nutrients they require to absorb water.

Place Your Young Poinsettia Plant Into a Container

Plant the poinsettia into the container with the root system being fully covered by the potting mix. The root system should already be strong if your poinsettias are being grown from a cutting.

Water the Poinsettia

Poinsettias require ample amounts of water, which is why the soil should never dry out. Make sure that you see some water leak through the drainage holes. The soil should also be checked on a daily basis. In the event that the leaves are dry after the first week, you can spray a fine mist of water to keep them from wilting.

Place the Poinsettia in the Greenhouse

The best place to put poinsettias in a greenhouse is toward the south-facing wall.

Cover the Poinsettia

Your poinsettias should be covered by cardboard boxes around 14 hours every night. This box shouldn’t touch the plant’s leaves.

Set the Greenhouse Nightly Temperature

The nightly temperature for your greenhouse should be relatively warm at 60-70 degrees Fahrenheit. When paired with the right amount of light, you should notice the plant starting to develop its distinct hues.

Continue to Cover the Plant

Your plants should remain covered until the holidays arrive. From here, you can display your beautiful poinsettia plants or sell them to buyers searching for a great holiday flower.

9 Greenhouse Poinsettia Mistakes to Avoid

Poinsettias require very specific conditions to grow correctly, which are detailed below.

greenhouse poinsettias

1. Too Little Mist Early

When you’re growing poinsettias, you shouldn’t use too much mist during the growth period. However, the initial 3-4 days are essential if you want your poinsettias to thrive. At this stage, the cuttings can wilt easily. Spraying a considerable amount of mist during the first few days should allow the cuttings to become better established. If they wilt early on, the plant could develop leaf drop issues.

2. Phosphoric Acid

Even though acidifying irrigation water is important for these flowers, growers oftentimes make the mistake of using phosphoric acid. As mentioned before, this acid is easier to handle than nitric or sulfuric acid.

It’s also much more soluble as a nutrient. On the other hand, phosphoric acid will get rid of the waxy cuticle that’s situated on the surfaces of the leaves. Over time, the leaves can be exposed to sun burn, pathogens, and other stresses.

3. Too Much Mist in Week Two and Three of Propagation

Another potential problem you could encounter occurs if you apply too much mist during the second or third weeks of propagation. If you reduce misting after the fourth day of growth, roots will form around the callus. These roots are necessary to allow the plant to feed. If the callus doesn’t have any roots surrounding it, you’re over-misting the cuttings.

4. Fungus Gnats

Fungus gnats can develop during propagation and may continue in the latter stages of growth. These gnats are typically considered nuisances but can be pests when it comes to poinsettias. Gnats are known to feed on poinsettia tissue. Their main area of focus is the callus tissue. This problem can eventually lead to Pythium, which is a type of parasitic fungus that causes these plants to die. With the right tools, fungus gnats can be controlled.

5. Pinch Preparation

When growing poinsettias, pinching is essential to manage the finished plant’s quality. The number of bracts can be controlled at this stage of growth. Make sure that the internodes remain short to keep the bract height even.

If you want to maintain internode spacing, you can use a growth regulator spray. If you want the bracts to grow at a salable position, it’s highly recommended that you focus on managing the length of leaf internodes as well as the timing of the pinches.

6. Post Pinch Stress

In the time soon after the pinch occurs, new developing branches are growing, which is when the axillary shoots should be properly established. At this stage, the wrong greenhouse conditions can cause some axillary shoots to become stunted or blind. Make sure that humidity levels are high and that light and heat levels are low, which ensures that branches develop normally.

7. Spacing on Time

Every poinsettia you grow will be in competition for available space and labor. Among the more common mistakes that growers make with poinsettias is spacing them incorrectly. If these plants don’t have much space between them for a lengthy period of time, the outside bracts or lower branches can become stretched, which will eventually result in them being weakened. Keeping plants too close together can also result in increased height.

8. Managing the Fertility Level

While poinsettias grow, they require more nutrients. By properly monitoring your plants and the conductivity, you can determine when the plants are using less or more fertilizer than usual, which will help you maintain proper feed levels.

Once poinsettias have been planted and pinched, a stage of rapid growth will occur, which leads to higher feed consumption. After the flower initiation takes place, these plants consume a lower amount of fertilizer for a short period of time. Keep in mind that conductivity readings will be at their highest when the plants are about to finish their growth stage, which can cause outbreaks of Pythium.

9. Pythium

As touched upon previously, the main issue that causes poinsettias to die early is Pythium. Not treating this issue can cause serious problems with your crops and may eventually result in substantial crop losses. In the event that you apply metalaxyl drenches to keep plant diseases at bay, you should be cautious about the efficacy of this treatment. Many Pythium strains are resistant to it.

Poinsettias are believed by many to have some of the most beautiful blooms of all flowers. However, a considerable amount of skill and work is required to grow these crops in a greenhouse. Because of the many advantages these crops provide to greenhouse growers, you should consider planting them for the holidays.

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Posted by Dominic O'Donnell on December 19, 2022

Sensorex is a global leader in the design and manufacture of quality sensors for water quality and process applications. The company offers more than 2000 sensor packages for pH, ORP, conductivity, dissolved oxygen, free chlorine, chlorine dioxide, UV transmittance and other specialty measurements, as well as a full line of sensor accessories and transmitters. Its expert technical support engineers solve analytical sensor challenges with custom designs and off the shelf products.

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