Can heat mat be used continuously even for established plants?

[our3swimmers]

Hi, I am new to semi-hydroponics and have read every single article in Ray's site a few times already and followed his prescription faithfully. I have transplanted a few phals and catts. I started off by putting the phals on top of a bank of 8 T5 lights. This acts as a heat source from the heat that the lights generates; like using a seeding mat. The light level is very much lower no top, mainly coming from grow light reflecting by the walls nearby. The leaves are firm and the roots look healthy. New roots began to grow as well after a couple of weeks. I then moved the phals under the T5 lights about 15 inches away. After a few days, some of the bottom leaves began to limp. I figured that must be due to high light level that the underdeveloped root system is not able to support. I then moved the plants up on top of the lights and the leaves were firm again.

Here comes my question. Will it be detrimental to the plants if I put a seeding mat under the phals and catts under light continuously? It looks like that the heat from the bank of light increases the moisture/evaporation of water from the reservoir. If that is advisable, I plan to build a temperature controlled heat mat for all my semi-hydroponic plants. Does anyone have any experience with that? Does the humidity matters for S/H? My current RH is about 45% and temperature is relatively constant at around 65 degrees. My grow area is in a basement. The catts have just been brought in from the outside to give them a 10 degrees or more daily variation in temperature. My grow area has little daily variation in temperature. Thank you in advance for all you experts out there!

[estación seca]

Welcome to the Orchid Board!

I think your Phals might have wilted due to higher temperatures under the lights, rather than higher light levels. Do you have a fan over the plants? Heating is from not only heat emitted by the fixture, but light striking the leaf and being absorbed. Without good air circulation leaves heat above ambient temperatures.

Higher temperatures lead to more evaporation and the roots need to supply more water. If the roots can't do that the plant wilts. Too-high light with phals generally causes leaves to become paler green, then yellow, then bleach; high light will do this even at cool temperatures.

Ray writes heat mats should be used when establishing plants in S/H to keep the root zone warm and encourage new root growth. If your plants are still establishing, then yes, use the heat mats. Once established, heat mats may allow plants to grow more through the winter in the basement, but are otherwise not necessary at your temperatures.

Phals and many Catt hybrids don't mind being warm all year.

Some Catt species need to stay warm all year. Some Catt species bloom better with winter night temperature drops.

Phals will stay in continuous growth if kept warm all year. Many people say Phals bloom better if they spend a few weeks in the fall with much cooler night temperatures, so constant warmth might affect your flowering.

My one no-ID hybrid Phal in S/H under my conditions is growing rapidly with RH 40%-60%, much of the time at the low end of that range. It is big enough to bloom. Temperatures in that room are almost always above 75 at night an 80 during the day. I will put my plant outside when our weather cools even further to stimulate bud formation, but will not let it freeze.

Catts tend to do well with even lower RH than Phals.

Your ambient temperature and light will probably be your limiting factors for growth, and your Catts and Phals will grow better during your warmer and more humid summers. Most basement over-winterers in cold-winter climates aim to keep their plants healthy, rather than keep them in active growth, due to the increased cost associated with more heat and light.

[Leafmite]

If your Phals do better with the bottom heat, why not keep using it? I have cooler home temperatures in autumn/winter so I bought a heat mat and miniature greenhouse for my two Phal. seedlings and the plan is to keep the mat plugged in until the warm weather returns.

[mtorchid]

Originally Posted by Leafmite

If your Phals do better with the bottom heat, why not keep using it? I have cooler home temperatures in autumn/winter so I bought a heat mat and miniature greenhouse for my two Phal. seedlings and the plan is to keep the mat plugged in until the warm weather returns.

I agree with Leafmite, I also use a seedling heat mats, especially for Phals, in colder months. In addition to RH, root temps are also important and the act of evaporation in SH will also cool the roots. Your phals and Catts might do "okay" without it, but higher temps would simulate their natural environment and they would most likely do much better.

[our3swimmers]

You are probably right, estación seca. I do not have a fan over the plants. Most of the leaves under light is very slightly warm but they all have been growing quite well before converting to S/H. The leaves are not being bleached or turning light green so I suspect the light level is not too high.

I guess I'll take Leafmite's suggestion keeping the bottom heat on. Thank you for being so generous in your suggestions and comments.