Wall o' Water

Protecting Bedding Plants from Late Frosts

Every gardener goes through the same syndrome every spring. You know what I mean: your tomato seedlings have outgrown their little peat pots and have gotten leggy, too tall for your grow lights. Worse, they're starting to look a tad peaked. Still, the climate refuses to cooperate: even though average last frost was a week ago, the weatherman's talking about high twenties in the nights ahead. Even here in the deep south, I've been able to find a couple of sun-faded, battered carton exactly what we used during Denver's unpredictable springs; we gardener’s savior called a Wall o’ Water.

What’s a Wall o' Water?

It’s a flexible circle composed of plastic tubes two inches in diameter with open tops and closed bottom. It makes a circle 18" across and 18" high, all heavy-weight green plastic. When you fill those tubes with water, the whole thing stands upright. "So what?" you say. Well, the important thing is important is what’s inside: a tender little bedding plant. The plastic wall protects your babies from chilly winds, and the water holds latent heat overnight. That prevents whatever’s inside from exposure to late-season freezes. The company claims that one will protect a plant to 16°F (-8°C), though they don't say for how long. On the other hand, I’ve never seen one frozen solid, or seen a bedding plant killed by frost when surrounded by one. I have seen plants get fried if you leave one in place once the danger of frost has passed.

A Wall o’ Water operates on simple physics: water is more efficient at holding heat than air, so the device forms a sort of tiny “heat island” around whatever is inside. You fill the tubes part way at first so the top leans inward, teepee-like, for added protection. When it gets warmer you fill them all the way so the thing stands up straight in a cylinder. The trick is to fill them in stages, so the plant has the most protection when it’s smallest, then the top is open to let in sunlight and warmth as the plant grows. With a Wall o' Water, you can put out bedding plants as much as a month in advance without needing a cold frame.

Once the danger of frost is over, I’ll squeeze the tubes to empty out enough water that I can lift it off the plant, and then pour out the rest of the water. We make a point of letting them dry thoroughly before putting them in storage.  If treated properly, they will last almost indefinitely.

Summary:

PLUS: plants can go in the ground even if there's still danger of frost
MINUS: you can fry a plant if you leave them on into the hot season
WHAT THEY'RE SAYING: A Wall o' Water gives bedding plants get a head start, "average last frost date" be damned!

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