Ask the Gardener

Ask the gardener: The curious case of the ice spike

CorrespondentFebruary 7, 2014 

An ice spike can develop when a shallow pool of water, such as a birdbath or water bowl for pets, freezes rapidly.

COURTESY OF L.A. JACKSON

We have a birdbath in our garden, and at the beginning of this year when it got so cold, the birdbath froze, and we found an odd, triangular, slim chunk of ice rising up out of it at an angle. The birdbath is in the open, so nothing could have dripped into it, and the piece of ice didn’t look like it just dropped in. I’ve never seen anything like it before. I wish I had taken a picture of it. Do you have any idea of how it could have formed?

Elaine Terry

Durham

The frozen phenomenon that rose from your bird bath is commonly called an “ice spike.” It usually occurs when a shallow pool of water – such as your birdbath or an outdoor water bowl for pets – quickly freezes. Water freezes from the top down, and occasionally this solidification is uneven across the surface, leaving a small hole. Since water expands when it freezes, some can be pushed through the hole, which, when exposed to very cold temperatures, begins to rise up as a tube of ice. This tube will continue to grow until the hole the water is being forced through freezes over. If this cold construction goes on long enough, the result is an ice spike.

If you have a bit of mad scientist in you and want to repeat this effect, you can make small ice spikes by pouring distilled water into a plastic ice cube tray and putting it in the freezer. I haven’t tried it myself because I use such ice for drinks, and I don’t want to poke my eye out.

Paw paw pollination

I live near the Neuse River Greenway and believe I have identified several paw paw patches along the river banks. They bloomed very well this past spring, but I saw no evidence of fruits. I know that paw paws can be difficult to pollinate. I have read that hanging some scrap meat could attract varmints and insects that could assist in the pollination, but I am not sure if other users of the greenway would appreciate that. Do you have any other suggestions, or should I just be patient?

Thompson Brockmann

Raleigh

Paw paws can be real bears to bear fruit. I know gardeners who have resorted to using small brushes to physically move pollen from one bloom to another. Call me lazy, but you won’t catch me doing it. And even though flies and beetles are the main visitors to paw paw flowers, which have an unpleasant smell, you won’t find me hanging cheap steaks in trees to help pollinate them, either.

Brushes and stinky meat might not work anyway, because these trees are self-incompatible, meaning paw paws only produce fruit when pollinated by paw paws that are genetically different. So if the trees you saw along the river originated from the same parental paw paw, that could be the reason for failure to fruit. For folks wanting to plant paw paws and enjoy their fruit, this inhibition to inbreed can be solved by simply selecting two different cultivars.

Fragrant winter plants

What would be on your short list of suggestions for plants that not only bloom in the winter but are also fragrant? I know such plants exist, but I wanted to see your suggestions to see if I am on the right track for this area.

Lynn Curry

Chapel Hill

My short but sweet-smelling list includes winter daphne (Daphne odora; grows about 4 feet tall); witch hazel (Hamamelis x intermedia; 6-18 feet); winter honeysuckle (Lonicera fragrantissima; 8 feet); and wintersweet (Chimonanthus praecox; 10-15 feet).

L.A. Jackson is the former editor of Carolina Gardener Magazine. Send your garden questions, including the city where you garden, to: askthegardener@newsobserver.com.

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