Growing Concerns 597: African violet, Jade, winter blooming

In this issue:

Arican violet dislikes cold draft?
Secret to jade plant's bloom
Protect poinsettia between store and home
Snow shoveling: Shapely gardener, smashed shrubs

When winter winds blow tropical houseplants suffer

I received an African violet as a gift. It seems to be a gift magnet. Since I got it everyone wants to give me advice how to grow it!

Many of the tips have to do with watering. Is it really so important how I water it? - M.M. -

Dear M.M.,

They're very popular so there are many people with African violet experience. Yet the fact that they grow well for so many people is testimony to this species' ability to deal with varying conditions. So there's more than one right way!

It is important that water you pour on the soil or into the saucer to be drawn up into the pot is room temperature, not cold water. This plant is native to Tanzania, where temperatures rarely fall below 60 degrees F. Cold rain and cold soil just don't happen in Tanzania. So the species never developed any ability to deal with cold.

African violet roots bathed in cold soil or sitting on a chilly windowsill often die and then rot.

Cold water is not good for the leaves, either. Where it touches a leaf, a white spot is likely to develop.

For illustrations and more on diagnosing cold damage, see What's Up 192: Jade cold cut back.

It's not true that African violet foliage must stay dry. They're "watered" by rain from above all the time in their natural setting. So you can water from above or below. It's also accepted practice to clean the leaves during non-blooming periods by inverting the pot over a dish of mildly soapy water, dipping the leaves and swishing them clean.

(Just how cold must water be, to actually damage a plant?
Sponsor us and Growing Concerns 751 can
jump to the head of the line to be posted.
That issue explodes myths as it
explores irrigation water temperature.)

For more about cold and houseplants' low temperature limits,
see Growing Concerns 680.

Jade surprises her with flowers

I've had a jade plant about 10 to 15 years. I put it outside in the sun every summer and it's very large now. I was amazed this fall when I brought it inside it started flowering after a few weeks. Is that quite uncommon? - S.M. -

Dear S.M.,

No, not uncommon for someone who leaves a jades out long enough in fall that the plant feels decidedly cool temperatures and lengthening nights for a few weeks.

It's all chemistry. While it's in the light, a plant uses carbon dioxide and releases oxygen. At night, it burns oxygen to convert the sugars it made during the day into energy to fuel basic life processes. Different chemical reactions occur at night than during the day. In fall night reations happen for longer hours at lower temperatures, so the by-products are different. Given enough time, those cool, night-formed chemicals build up and the plant is spurred to produce flowers.

Our jade flowers pretty regularly after coming indoors in fall. One year we were delighted to see that it flowered on one side but not the other. Delighted, because we're teachers and saw it as a perfect teaching example.

This jade sits on an open-sided but covered porch. It is very large, and that year had gotten even larger than normal so that one side, facing out, had "bellied out" so far that it was not under the roof that sheltered the rest of the plant. That fall, it was warmer than usual, so the part of the plant under the roof didn't experience enough cools nights to spur flower production. (A roof, even over a wall-less area, bounces heat back to the ground that would otherwise radiate away each night.) But the outer portion of the jade that was exposed to more cold, for more nights, did form flower buds.

For more about this effect, and other long night plants, see What's Up 191: When long nights spur bloom

Short reports

Say "paper please" when you buy a poinsettia.

Don't let an uninformed salesperson ruin your poinsettia or other holiday plants. Such plants must be protected from the change in temperature as you take them home and should be wrapped in paper to face the weather.

Insist that the plant be wrapped, to trap some insulating warm air around it. Don't accept a plastic wrapping, as moisture can condense on the inside of plastic and that water can cool very quickly, damaging leaves and flowers.

The same is true for almost all houseplants, which are tropical species without any tolerance for cold.

Green thumbs up

to snow shoveling as a way to stay in shape for next spring's gardening.

Green thumbs down

to tossing big loads of heavy, wet snow onto the brittle branches of shrubs such as bluestar juniper.