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Indoor plants need fresh air too. Here’s how to give it to them.

  • Author: Jeff Lowenfels
    | Alaska gardening
  • Updated: November 15
  • Published November 15

Mail call. Lots of questions with general application here, starting with why do you need to keep plants where there is good air circulation. A great question. I always talk about air circulation, but a reader wants to know a bit of the science behind it.

There is usually a microclimate around plant leaves, created by a thin layer of still air. It is called the boundary layer. If it's too thick, at least two things can go wrong.

First, CO2, which is needed for photosynthesis, has trouble getting through this layer to enter the leaves. The plant can't make as much energy as it may need. It doesn't operate at full capacity. Second, the plant doesn't take up as much water because the vapors released during photosynthesis are still inside the leaves, which messes up the plant's "drinking" system. This system involves pulling nutrients into the plant.

As a result of this layer, then, plants don't get the nutrition or energy they need. What a shame, when all it takes is a bit of air movement from a cheap fan to move this microclimate aside so the plant can operate properly.

Next, a question I get every year at this time: Do you fertilize houseplants during the winter? The standard advice has always been that you do not because supposedly plants stop growing in the winter, but that is wrong. You fertilize plants (actually you feed the microbes and they fertilize the plants) when they need it. And that could be at any time of the year, especially since I know all of you readers have set up light systems for winter growth!

The better question is what to use on your plants. For my money, a quarter-inch layer of compost keeps our houseplants in good shape without needing any supplemental fertilizers. Kelp meal is also a great microbe food that helps keep plants healthy.

If you buy fertilizer, make sure it is organic. If your plants are flowering types, you want to have a bit more of the second number on the package trilogy, phosphorous, than on the first number, nitrogen. If your plants do not flower, you want a slightly higher first number.

Next, what is the best way to grow paper whites? Paper whites, a type of narcissus used for indoor forcing, are always easy to grow. Pot them in well-draining potting soil. Their necks should stick out of soil. The big tip here is to then keep your pots for a couple of weeks in a dark spot where the temperature is between 50 and 60 degrees. This will allow them to develop some roots before they are exposed to light. Once this is over, the heat from the top of the refrigerator or a seed heating mat will speed up growth and blooming.

Of course, you don't have to use soil for paper whites. If you can support bulbs above water, so the base is just touching it, the plants will develop roots and top growth. Don't worry about bulbs that have crooked growth developed during storage. This will straighten out once they start getting water and better light. By the way, don't store these plants in the refrigerator as it is too cold. On top of the refrigerator is a much better spot as they like the warmth.

OK, an urgent call for help, which others might need: "Which is the Thanksgiving cactus and which is the Christmas or the Easter one, no Latin names, please, just an easy answer." (As if!)

The simple answer is that the Thanksgiving varieties of Schlumbergera have leaves with jagged edges. The Christmas varieties of Schlumbergera have rounded edges. However, you should be able to tell by blooms. They are named for a holiday for a reason, right?

The reason you may be having confusion, however, is because they are induced to bloom by both diminishing day length and cooler temperatures. Normally 55 degrees or so will trigger them for their individual holidays. However, if they get below 50 for a while, they can decide to celebrate early.

Alaska Garden Calendar

Turn plants: Plants grow toward light. Turn them once a week or so to make sure you get even growth.

Thrips: Are these little flies still annoying you? Try putting one of those Mosquito Dunks — the kind you can put into ponds to kill larvae — into the water you use on your plants. Or place newsprint on the soil surface to make it difficult for the adults to fly in and out. Also, cut back on watering so the surface dries.

Family Wreath Making: Alaska Botanical Garden, 6 to 7:30 p.m. Nov. 20, fee required. More information online or call the garden at 907-770-3692.

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