Hello, I am growing Poinsettias in Montana, and have a few questions.
1. Recommended greenhouse temperatures; does this refer strictly to air temperature? Is there a range of recommended soil temperatures?

For our northern conditions what varieties are best? We are having problems getting pinched plants to grow long enough shoots before flower initiation begins. We have used Freedom the past few years; we grow unpinched pots in 7, 8 and 10” sizes, and pinched pots in 4 and 6” sizes. Generally, our un pinched pots finish well, but not the pinched pots, especially the 6” We like the darker leafed varieties the best, and grow red, white and pink.

Last year we were in a heat wave when it was time for our rooted cuttings to ship. Neither we nor the supplier can control the weather, but we are curious to know to what extent this can affect the crop. It was over 100 degrees the week they came in, wet wilted in the boxes. After planting it stayed in the high 90’s and 100s for several weeks. The plants developed really thick roots, but plant height and bract size was reduced by nearly half!

Considering our northern conditions, would a combination of Florel and a light pinch be a better approach than pinching a 6” pot to 5-6 nodes after rooting out? THANKS!!

First let's talk about the height issue. Excessive heat can certainly create a lot of problems for your crop. The key during those really hot periods is to minimize stress to the plants as much as possible. They should be shaded and not under any moisture stress. Here's where the question about soil temperatures come in. During a period of excessive heat the soil can actually warm to such a high temperature that it literally "cooks" the roots. Syringing the plants during the hottest part of the day with cool water will help cool the root zone and reduce plant stress. Ideally we like to see soil temperatures at about 72F but obviously the soil temp may be warmer than this in the hottest part of the year. During cooler months the soil temp may be colder than this (60's) but striving for 72F is a good target. Heat stress can have an affect on plant height if the roots become damaged and diseased and can't support healthy top growth.

If you say the roots were still vigorous and healthy than we should talk about scheduling. The phase between pinch and flower initiation is what we call the vegetative growth phase. Essentially the length of this phase determines the final height potential for the plant. If the phase is too short because of a late pinch the plant will be shorter. Using Freedom as an example, we recommend for a medium vigor plant that you allow at least 20 days between pinch and flower initiation in your northern climate. Because Freedom initiates earlier than most cultivars (approximately Sept. 15th) this means you should have Freedom pinched by about August 25th. If you haven't already referred to our Crop Scheduling this is a great tool to use for crop scheduling and offers specific recommendations for planting and pinching dates for different regions of the country and the different growth rates of various cultivars.

Regarding your Florel question, we have found that most varieties benefit from an application of Florel because it does enhance break count after pinch but it also enhances uniformity of the breaks. Florel does also offer some mild growth regulator effects so if you typically use any early growth regulators such as B-Nine/ Cycocel, using the Florel will probably eliminate the need for at least one application in your regime. If you are pinching to 5 or 6 nodes now that is usually what we recommend for a 6" container. Again it may not be pinching techniques but maybe a scheduling and pinch timing issue rather.

Let us know when you pinched....if the dates need to be adjusted that is easier than choosing new varieties. If your pinch was timed correctly and that wasn't the reason for the reduced height than we can come back with some recommendations for other cultivars that may suite your needs better.

Thanks for getting back to us!