Features Crop Protection Inputs
GREENHOUSE GROWER NOTES August 2006 2

Poinsettia preview – getting the crop out of the blocks quickly and smoothly!  How we handle the cuttings for the first 4-5 weeks after transplanting usually plays a role in the quality at the end.

By the time you are reading this article, all of the early season poinsettias will have been planted. It seems hard to believe!  Time sure flies by when we are busy and having fun!

Pricing aside, the poinsettia over the past few years is the crop about which more growers complain or possibly hate than any other.  While a well-grown poinsettia crop at shipping is a beautiful site to behold, a poorly grown crop can be downright ugly. I might be stating it too bluntly, but there have been many poorly grown crops in the past few years and there really is no excuse for lousy quality. We wonder why the market is soft. Yes, overproduction is a factor, but don’t discount poor quality at the retail level or poor performance in the homes of consumers as being major factors.

Growing quality poinsettias is all in the details. With fewer poinsettias being grown this year compared to last year, there seems to be no reason why we can’t focus on improving our quality. Growing poinsettia should be fun! But it all starts right at beginning with planting.

Cuttings – It is important to be fussy with which cuttings you plant. Throw out the small, spindly, or poorly rooted cuttings. If there are signs of Pythium root rot present in cuttings in a strip, discard them as the crop will become uneven, make the growing decisions you have to make more difficult, and cost you more money in labour and pesticide expenses than simply throwing out the cuttings in the first place.

Avoid the temptation to be “penny wise but pound foolish.”  In the end, a second grade cutting finishes as a second grade plant that costs you just as much to produce as a number one.

Potting/Planting – Cuttings rooted in oasis need to be planted deeply to prevent drying of the oasis and to provide better stability for the growing plant. Poinsettias grow best in a coarse, well-drained media to help avoid root rot problems. This ensures good aeration even when the media is at maximum water holding capacity.
It is important to water well as soon after potting as possible to avoid wicking of moisture from the oasis.

Keep the moisture level high for the next five to seven days to make sure all the cuttings get rooted out evenly into the adjacent media. When outside temperatures of 30ºC and higher are common, it very important to water the floors and crop lightly from overhead several times a day.

Last year there was considerable unevenness in the rate of plant establishment because growers tapered down the moisture too quickly. Some cuttings were slow at rooting out because of being too dry. This means that the media should be watered thoroughly at planting and light overhead watering be done one to two times per day to keep the upper 5 cm moist.

High humidity is an important benefit that reduces transpiration losses. This point can’t be overemphasized when setting out on concrete floors or benches in glasshouses. Remember that the environment in many greenhouses when first planting poinsettia is comparable to a desert. Only cacti thrive under those conditions!

Providing a transition environment from that of the propagation bench to that of the production area is the key role of utilizing plenty of water during the establishment phase.

Temperature – To ensure uniform establishment, it is important that the crop be kept warm at night. The minimum night temperature at time of establishment and growing on should be 22–24ºC.

The early-response and compact cultivars need to be grown warm to establish uniformly and achieve the necessary growth and plant size before the critical daylength is reached for flower initiation. The first roots should be visible at the bottom or side of the pot in five to seven days after transplanting.

Light – The cuttings should be shaded when first transplanted to reduce the light level and the plant temperature until roots become established into the growing media and begin absorbing water from the growing media. When using an automated shading system, the critical time for the first few days is between 10:00 and 15:00 h when the sun is at its sharpest. The aim should be to condition the cuttings to their new reality! Shading compound should be removed by the end of August. Light intensity and daylength quickly begins to change. Don’t get caught daydreaming of an Endless Summer!

Fertilization – Begin within four to five days of planting to water lightly with a fertilizer like 20-8-20 or comparable product.  Phosphorous is important for root growth and development as well as for photosynthesis. Poinsettias respond best to constant fertilization but are intolerant of high media EC. A nitrogen level of 200 ppm or an EC in the 1.8–2.0 range is quite adequate to maintain a young actively growing poinsettia crop under most production systems.

Ammonium-based nitrogen is also important because it encourages leaf expansion and softer growth, which is beneficial for lateral shoot development after pinching. Check the EC and pH of the media biweekly. Lowering the EC for the first 7–10 days after pinching avoids potential problems because the plant after pinching has lost most of its active leaves, and relies on stored energy to begin pushing out the lateral shoots. Resume fertilization once the shoots begin to elongate.

 Pinching – Pinch when the crop is ready, not when you are ready or by the date on the calendar! As a guide, most cuttings are ready for pinching 15–18 days after planting. Plants begin to get leggy if delayed much longer. Every day pinching is delayed is one less day of good weather to create strong vigorous lateral shoots.

Check each cultivar carefully to determine how many of the lower nodes produced on the cutting on the stock are blind or appear to have misshapened lateral buds. If there are two or three questionable lower nodes, and the goal is to have five or six strong shoots at Christmas, plants should be pinched to eight to nine nodes. This is always more of a concern with the dark leaf cultivars.  There is nothing worse than pinching to six nodes and only getting an average of 3.5 shoots per plant.

Although it is not necessary, removal of the top one or two leaves remaining on the cutting is recommended, especially if these are large, young leaves that developed since planting. Leaving these leaves provides greater shade of the lower breaks and tends to suppress the lower lateral shoots because of the gibberellins produced the remaining young leaves are translocated downward.

Plant Growth Regulation – Rooting stations generally apply PGRs on the rooting bench to prevent stretching that occurs 10-12 days before shipping of the rooted cuttings. Checking the cuttings closely beginning around Day 12 after planting for stretching of the new growth and of the lower lateral shoots is one of the most important activities you can do as a grower.

Keeping the internode spacing close together and preventing the lower lateral shoots from elongating prior to pinching is key to uniform breaking and shoot development. The timing of a 750/750 ppm Cycocel/B-Nine spray is usually four to five days before pinching. Keeping the first node short (1.5–2 cm) on the developing lower shoots forces them to thicken, making the stems stronger and less prone to stem breakage at shipping after the large bracts have formed. Application of a second combination spray four to five days after pinching is recommended for the vigorous cultivars. It can be used on all cultivars if pinching is done in August, but for the less vigorous cultivars move quickly, providing only a “dusting” of PGR.

Remember, achieving a little extra height later on is easy to do but taking away extra height is impossible! If you are located in other regions of the country, the timing will be different because of latitude and weather conditions.

Root Rot – Pythium, as a pathogen, is always of concern but doesn’t have to be … well, maybe it does if the crop is grown on concrete floors. The first line of defence: if there are strips of cuttings with root rot when planting, discard them! It is cheaper to throw a few away at the beginning than to start off with the disease present.

Check roots biweekly for the presence of root rot. Drenching with a combination of Truban (Pythium) and Quintozene (Rhizoctonia) within the first week of planting is a good preventative measure. Relying on the use of Subdue Maxx to control any outbreaks later in the crop is a good resistance management strategy.

Spacing – Keeping the plants pot tight until the lateral shoots have begun to develop after pinching provides a better micro-climate around each plant as well as more efficient use of water and fertilizer.

Don’t space until the shoots have begun to develop nicely (1–2 cm) long as it helps keep the lower shoots more upright. This is more critical for some of the dark-leaved cultivars.

Spacing on time and providing adequate spacing minimizes stretch. Allowing the light to come in all around encourages the plant to fill out instead of stretching. Spacing plants more than once costs money in labour, but if the crop needs space because it is beginning to stretch, give it space. The crop will respond in a positive way to the added space within a couple of days.

Summary – Think of the following analogy. Starting the poinsettia crop is like all the well-conditioned athletes who run the 100 m sprint.  For these runners, getting out of the blocks quickly and smoothly is key to a good race. The same is true of the poinsettia crop: getting the cuttings off and growing quickly after transplanting improves the odds of finishing with a quality crop.  Lots can go wrong as we will discuss next month, but how we handle the cuttings for the first four to five weeks after transplanting usually plays a role in the quality at the end.

Let’s all grow a crop of which all of us can be proud. 

Wayne Brown is the greenhouse floriculture specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, University of Guelph, in Vineland. • 905-562-4141, ext. 179; wayne.brown@omafra.gov.on.ca.