Tips for Greenhouse Growers
E. White Smith
Reprinted from the Vireya Vine, June 2003
Here are some tips for greenhouse owners I have learned over the years. If you have a greenhouse try covering the whole outside with poly-plastic in the winter. The plastic stops water leaks and seals holes. If the greenhouse is glass it will keep slipped glass from letting in cold air and rain. I don't know what would happen if it snowed and you had to get out and pull the snow off. Anyway, it works great for us and saves a lot of heat.
Holes or cracks or slipped glass you can or can't reach. The "spray-can foam" works great, and after a couple of days you will be able to get it off your hands and also will be able to go back and trim the hardened foam with a sharp knife so that it looks better. If you have plastic lenses in your glasses, be careful - this spray foam will eat into the lenses if it gets on them. It is great stuff for fixing rotted wood you don't want to replace right away. When you are using this spray foam it comes roaring out the long tube and sometimes globs of it fall down. It is hard to get off vireya leaves - and shoes, shirts, hair, etc, and if you do very much you will have it all over yourself. It has a mind of its own.
Okay, the spray foam works but sometimes we want to kill things. The "things" I really don't like are small weed-type things called "pearl wort" and "liver wort." Both of these small plant/things would grow just fine in the greenhouse in pots, on steps and on paths, both inside and outside. Pearl wort looks almost like a moss but is usually a brighter green. It has very small flowers and must make a lot of seed because it will come up everywhere. Liver wort is a small plant that grows flat on the surface, has almost round scale-like leaves and must somehow make seed because it also comes up everywhere once it gets established. Liver wort will look like some ferns do in their first stage of life (ferns go through two major stages) so you might think that they are baby ferns. Both of these weeds are hard to get rid of. Weed killers like Roundup do not work. But, simple, cheap vinegar does work. Just spray it on the plants straight as it comes out of the jug. It will also kill moss so be careful if you like moss. Vinegar, vinegar, vinegar, I just love it because we had liver wort growing on an outside path and even if I scraped it off with a shovel it soon came back. And, yes, the vinegar might take a couple of tries to get the job done for sure.
If you have a greenhouse or like structure, you should look carefully to see how much light comes in from the north (south side, of course, if you are in the Southern Hemisphere). You may be able to save heat by not having clear glass or plastic on that side. We now use sheets of one-half inch (1.25cm) insulation foam on the north side of our glass greenhouse and hold it in place with the spray foam. We remove the sheets in the summer for ventilation - easy and much cheaper than replacement glass. Sometimes I can get this sheet foam with one side silvered which is even better. Wait, wait, should the silver side go outside to reflect the cold or inside to reflect the light?
E. White Smith, a member of the Tacoma Chapter, is the editor of the Vireya Vine, a newsletter for growers of vireya rhododendrons.