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Hortiscope: Double-paned clear walls best for local greenhouses

Q: I have two rows of arborvitaes that vary in height. Some are leaning and some bent almost at a 90-degree angle. Some of the stems are bent about halfway down. Unfortunately, there isn't room to stake them up because of a parking lot a few feet from the trees. Any ideas how we could save these trees? Would it help to trim them or take some of the bent tops off? Could we tie some together?

A: Yes to all of your questions. Tying them up should be a temporary treatment until new growth begins this spring. However, don't use twine or rope to do it as it may cut and girdle the stems.

Check the stems to be sure there are no breaks where they are bent. This often happens and the tree usually does a poor job of healing if that is the case. If you are unsure of what exactly to do, I encourage you to contact a competent tree care service to do the job. Look for an International Society of Arboriculture certified arborist when considering what tree company to hire.

Q: I would like to build my own greenhouse or purchase one. If I purchase a greenhouse, would 4 mil be thick enough for the walls or would double walls be better? If I built one, I was wondering if the panels that you see on top of buildings that are white and let light in would work for the walls and ceiling.

I am not sure if the panels would let in enough light and heat to grow plants. Also, do you know where to find the seeds on a geranium plant?

A: In greenhouse construction in this part of the country, double walls would be best. The white panels are acceptable for the noncommercial growing of plants. Clear would allow in more light, which we sometimes desperately need during the year. It all depends on what it is you intend to grow. Geranium seeds can be found at the base of the spent geranium flower.

Q: We just bought a flowering Robinson crab tree. What is a good fertilizer for it? Do we fertilize at first planting? Do we use an acid fertilizer?

A: No fertilizer! Plant the tree at the right depth, water it well and stand back to let nature take its course. If your soil supports weed growth, it will support the growth of this tree without any outside input other than water to get it off to a good start.

To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or e-mail