Re: greenhouse-tomatoes: Questions.

[john howell <howell@umext.umass.edu>]

Michael,

 

In determining propoer night temperature, we must think of photosynthisis and respiration.  During the day both photosynthesis and respiration occur.  At night there is only respiration.  If there is adequate light during the day, there should be enough photosynthate produced so there is a surplus at the end of a 24 hour cycle.  Respiration increases rapidly with temperature, so if temperatures are too high, there can be a deficit of photosynthate after a 24 hour cycle.  This is seldom a problem if night temperatures are in the mid to low 60's and day temps are in the mid 70's.  Higher temps can be tolerated if the days are long and clear or if supplemental light is used.  Warm temps speed ripenning.  Low temps slow ripenning.  If temps fall below 60, there is increases chance of blotchy ripenning or grey wall.  In our area we don't use supplemental lighting and most growers have the best rersults with night temps around 62 to 65, but this can be increased following an especially bright sunny day.

 

John Howell,

University of Massachusetts Extensioin, retired.

----- Original Message -----

From: Michael Pierce

To: greenhouse-tomatoes@Lists.MsState.Edu

Sent: Wednesday, November 03, 2004 10:08 AM

Subject: greenhouse-tomatoes: Questions.

I have a couple of questions that requires expert input.

 

I’ve always heard that, when pruning lower leaves, one should remove no more then three leaves at a time to reduce stress on the plant.

My question about this is; who says? Some of these lower leaves, although still green, look like they are adding stress to the plant. I would like to remove leaves up to the first cluster with tomatoes on it. This may require the removal of 6 to 8 leaves. Has anyone tried this procedure and if so, what were the results? What negative affects should I expect by doing this?

 

Next question has to do with temperature. I believe 64 degrees F is the magic low number. I have a hydronic heating system so the heat is pretty uniform throughout the greenhouse. In the past I’ve gone as low as 55 degrees F with no negative effect on fruit set but the hot water pipes are within inches of the root ball/buckets. I’ve recently learned that lettuce can be better controlled by monitoring nutrient temperatures and not so much ambient temps. Given that lettuce is all leaf, I realize that this practice can not be strictly applied to tomatoes. I’m wondering to what extent it can be applied. In other words, if we heat the solution and or the root ball to a suitable temp, how low can the ambient temps go? Then, what is a suitable root temp? Another question is why 64 degrees? Is it for the benefit of the flower, stem, or leaves?

 

Perhaps the researcher that came up with that number was basing it on what he thought was a comfortable temp for him to be working in the greenhouse!!

 

Any input would be great.

 

 

Michael Pierce

M & R Hydroponic Farms