Blind Shoots - Can They Form Flowers?
by Gaye Hammond
All rose stems have the potential to flower but sometimes they don’t. Failed flower development is a common problem in rose and is often referred to as “bud abortion” or “blind shoots”. Blind shoots are usually no more than three to five inches long, have thinner stems and have fewer leaves which usually have a lower chlorophyll content than leaves on stems that form flowers.
The formation of blind shoots in roses grown for the cut flower industry can cause great economic loss to growers and can bring about a 50 percent reduction in annual crop yields. In one of the earliest scientific studies on blind shoots (1934) the researcher found that blind shoots simply stop growing before the bud begins to develop. The question is why?
Photosynthesis (the process by which plants make food) is at its maximum when temperatures are between 68° and 77° F. Temperatures above 77° F can facilitate the development of blind shoots because there is a decrease in photosynthesis. The same is true for low temperatures. Roses often develop blind shoots when temperatures are below 59° F because the ability of the plant to make food at these temperatures are limited.
Low light levels can also result in blind shoot development because low light levels also lower the photosynthetic rate (less food = less growth). When low light conditions are present in combination with low temperatures blind shoot formation is at its greatest potential for formation. This partly explains why rose plants produce a high percentage of blind shoots during winter and early spring when short days with low light intensity exist.
The type of lighting also has an influence on the formation of blind shoots. For those in northern states that grow roses under lights in the winter, scientists at the Agricultural University of Norway found that using incandescent lamps caused blind shoots to form, while fluorescent lamps with a high red and far red (R;FR) ratio decreased the number of blind shoots. Their research found that blind shoot formation in rose is controlled by the blue-green pigment (phytochrome) in plants. This pigment regulates a plant’s developmental process.
Researchers at The Hebrew University of Jerusalem opine that removing the mature leaves from rose stems (a practice routinely performed in the spring in some parts of the U.S.) increases the number of blind shoots. Naftaly Zieslin and his colleagues suggests that it is mature leaves that produce photosynthates (sugars) needed for plant development and that removing the leaves results in less food for the plant and thus the formation of more blind shoots.
Under watering and overwatering can also cause blind shoots – but for different reasons. Under watering reduces the amount of food the plant can produce and also ability of the plant to move food through its vascular system. Overwatering can also cause blind shoots to form because ethylene gas forms in the stems inhibiting the transport of food to the new growth
Work done by D. S. Hubbell at the University of Arkansas Agricultural Experiment Station found that the vast majority (85 percent) of blind shoots simply fail to develop to the point that a flower will form. Work by these scientists support the recommendations of many rose societies and rosarians that blind shoots should be removed whenever they are found.