I work with paradox hybrid walnut rootstock clones. I wonder if I can keep them growing in the greenhouse with artificial lighting and keep the temperature warm during winter. Would they grow abnormally the following year? They are small plantlet about 3-4 inch (7cm-10cm) tall. It seems to me that the only reason plants go dormant is because the conditions for growth is unfavorable.....If i keep the conditions favorable, would they just grow year long? Thanks for any thoughts.
there are many species of juglans that require winter dormancy. Pecans (Carya illinoisensis) is a related species that requires cold unit to properly fruit the next year. I'm not a horticulturalist, but when I worked with young pecan trees for my masters we had to chill them for about 2 months. I would search google or another website for "cold unit or cold acclimation and juglans". If you can't find what you're looking for specifically for walnut you may want to branch out and search for black walnuts or pecans.
Many trees originating in temperate-subpolar regions will senesce if they are not given a dormancy period. The exact period required varies by species and in many cases the exact locality of the plant or genotype. Dormancy "can" be broken through plant growth regulator treatments but the effect on the subsequent growth and survival isnt very well documented. With first year seedlings of some plants it is often possible to push them through the first winter though it requires manipulation of cultural conditions and depends on when the plants were started etc. The safest method might be to induce or allow dormancy. Most likely the exact dormancy period would be based on chilling hours. If the chilling hour requirement were rapidly met (e.g. in a refrigerator or refreigerator/ freezer) it might be possible to then force the plant under conditions of warmth and long days to gain more growth in a set period of time. If the plants are to be used in research this might not be adviseable as the result could be influenced. It would probably be hprefferable to not allowing for dormancy
As inferred by the others, if the objective is to maximise the amount of growth plants achieve per year, then this will be achieved more readily if each of the stages of the annual growth cycle are optimised. Hence application of cold units within a cool store and returning to a phytotron facility or heated greenhouse with supplemental photosynthetic lighting, is likely to result in your plants achieving the most growth in one calendar year, and ensuring this growth is physiologically most "normal"
Thanks for the thoughts! My goal is trying to maximize the number of plants produced...but i'm fairly new to the field and we are late pushing plants to the field/hardening them (we replicate plants with micropropagation). So i wonder if we can catch up during the winter to get a little more plants....
I see no reason why you can not deflask micro-propagated plants into a heated greenhouse environment all year round (especially during winter at UC Davis). With your focus on "catching up in the winter" (I assume catching up in numbers of plants), as long as plants continue to grow during winter/spring in greenhouse, they can subsequently be transferred to outdoor production environment later in spring/summer when natural environment supports growth, and then plants will naturally respond to fall/autumn as seasons progress.
I think you can do this; I have similar experience in seed of walnuts (J. regia). We're planted the seeds immediately after harvesting without cold treatment. During the winter, they germinate and grow in a warm greenhouse and then in the spring when environmental conditions became desirable, Seedlings are transferred to the field and all show good growth during the growing season
If you plant them in the winter you should be able to grow them until you need to plant them out in the spring. However, if they are already planted and you just want them to keep growing through the winter you may have some issues. We have found that many temperate woody species do not grow through the winter in the greenhouse despite keeping the temperatures warm and an extended photoperiod. Instead, the trees still figure out that it is winter and start to scenesce. Plants that do this may resume growth again, but many of them die. We have found that we end up much further ahead by giving them their desired cold treatment rather than trying to trick them.
Now, if you figure out how to actually trick them, it may be a good idea...
For dormant period tropical plants should be get temperature between +0.5 - +7 C° , Chilling requirement for Jouglans genus is about 400-600h. please put your plant in cold green house for mentioned temperature and duration.
I think what you mentioned is right. what forces plants to go to dormancy is day length and temperature. I want to keep my plants growing in winter too. so I think its better that a little before start of cold weather and short days that stimulate the plants to produce ABA and etc., you start using the favorable condition which you mentioned. In this way according to what i studied they grow normal next year
I agree. You can keep your greenhouse warm and long days and plants will continue to be leafy and growing. Also, remove any other stresses, regular fertilization and watering if you want them keep growing. Having said this, it is still very likely that they will shut down upon planting in the field in spring (April in California) and wait for next winter to become dormant. We had mixed results with actively growing plants from greenhouse to field in June. Some of them continued to grow in field while others shut down. Need to learn more walnuts!
Lu, we should meet. We are only 30 minutes away. My email [email protected]
Walnut plants can grow year round by maintaining temperature and day length, however, for flowering and fruiting, I guess chilling requirement should be fulfilled.
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