What are Greenhouse GEMS?
Resource articles for all types of growers! Our information revolves around topics including:
Grower – Information & techniques that growers can implement now for successful crops.
Education – Concise explanations of necessary to know industry information for all grower sizes.
Maintenance – This month in your greenhouse to maximize production & longevity.
Seasonal – A variety of topics from growing to industry news.
Greenhouse GEMS – September 2021
Grower – Poinsettias Post-Plug Rooting & Pinching
Days 31-60 of Poinsettias (September – October)
The purpose of pinching is to remove the apical dominance of the plant which will then allow lateral branches to develop. Pinching is typically scheduled two weeks after planting the rooted cuttings. By then, roots should reach the edges of the pots showing that the plants are well established. Some growers will wait longer but it is best not to allow more than three weeks after planting before pinching your plants.
This pinch can be done with your fingers, snips, or a knife. This pinch will remove the stem tip from each plant. Try to leave 6 leaves under the pinch point. This will give you at least 5 full bracts when the plant matures. It often helps if one or two of the top, immature leaves are pinched off at this time also. This helps even branching for a more uniform plant and allows for more air flow and light to reach the inner canopy of the plant from where the new branches will emerge.
When pinching, it is also advisable to remove any premature stalks emerging from the bottom leaf nodes as these will affect the new branches and prevent a well-rounded plant from developing. These aggressive shoots often occur if one waits too long between planting and pinching. Keep in mind when removing these that you still want to leave 5 potential branches on the plant between the base of the plant and the point of pinch.
Here is a general pinching schedule that works well for most midseason (Late November/Early December) poinsettia cultivars:
| Pot Size |
Plants per Pot |
Planting Date |
Pinch Date |
| 8″ |
3 |
7/25 |
8/18 |
| 6″ |
1 |
8/15 |
9/1 |
Lastly, poinsettia sap is very sticky and is not toxic but could cause a reaction if a student has a latex sensitivity. If not using gloves, Avon Skin-so-Soft works well to remove latex from hands. Before wetting your hands with soap or water, rub them well with the Skin-so-Soft and then wash off after lathering with soap and warm water.
For more information check out our Seasonal GEM below.
Education – Why It’s Important to Test EC & pH
Why is it important to ensure proper pH and EC for growing poinsettias?
While growers are very adapted at rooting and growing poinsettias, ensuring optimal conditions will not only speed up rooting but also ensure a higher percentage of success. During the rooting process the cuttings are using up all their stored energy to generate new root and growth. Proper pH and EC values ensure optimal nutrient uptake and a friendly environment for the new roots developing. Failure to have proper pH may result in inefficient nutrient update while EC levels (salt levels) and burn new root hairs. Any damage to new roots at this stage are a big window for problems such as Pythium and Rhizoctonia root rots.
One way media pH and EC can get out of recommended levels is from water. Water testing should be done if your plants are showing signs of excessive pH or EC. Poinsettias prefer a more acidic media than many other flowering potted crops, care should be taken to keep pH within the preferred range of 5.8-6.5.
Maintenance – Winter Preparation & Heating Care
Items to consider for winter preparation:
- Inspect unit heating systems.
- Check for leaks, loose fittings.
- Turn system on for test run, make sure ignition occurs.
- Fans operate-check fan belt.
- Calibrate temperature settings.
- Ensure proper venting to outside of greenhouse and that air intake is clear.
- Upgrade horizontal air flow (HAF) convection tubing.
- Remove exterior shade.
Review University Articles on Greenhouse Winter Preparation below:
Greenhouse Heater Checklist-Virginia Tech Cooperative Extension Article
Heating System Maintenance-University of Massachusetts Amherst
Greenhouse Heating Checklist-University of Florida Extension
Seasonal – Poinsettia Pinching & Beyond!
Weeks 5 – 8 of the Poinsettia Guide
Week 5 – (September 6) First week after pinching.
- Keep moisture levels consistent
- Continue to feed at 250 ppm, using a 20-10-20 with each watering
- Keep humidity level high with good air movement
Week 6 – (September 13) Second week after pinching.
- Branching should now be evident
- Continue to feed at 250 ppm with each watering
- Test soil pH / make sure it reads between 5.8 and 6.5
Week 7 – (September 20) Third week after pinching.
- Remove any shade from over poinsettias
- Continue to feed at 250 ppm with each watering
- Space plants
- Be sure that no light can get into greenhouse at night
- Flower initiation will take place this week
Week 8 – (September 27) First week after flower initiation.
- Apply granular pesticide (Marathon) now as a preventative
- Continue to feed at 250 ppm with each watering
- Test soil pH / make sure it reads between 5.8 and 6.5
- Monitor yellow stick cards for whitefly
- Daytime temps should now target 75˚F
- Night-time temps should now target 65˚F
For other resource articles, helpful tips, or other Greenhouse GEMS, check out our Resources page for more information.