Dr. Curtis E. Swift

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December 6, 2012
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SWIFT: Winter-prepping of indoor & outdoor potted plants

This past Sunday I was dragging hoses to water the 400-plus lavender plants at my site in Mack. The field is 300 feet long and the plants are spaced at 3-foot intervals so it took almost three hours to water each of the four lines of lavender. The first watering involved the application of one gallon of water to each plant. This dampened the soil but did not penetrate very deep. I wanted the soil to be moist to a depth of 6-8 inches. Once I had moistened the soil, I planned on watering a second time so the water would penetrate deeper. So I turned around and walked back up the field watering each plant one more time.Temps were in the mid-50s when I was watering and a cabbage butterfly was flying around looking for flower nectar to feed on. The warm days had pulled moisture out of the soil increasing the chances of plant death by spring. Even with the moisture forecast for this week, I did not want to chance the possibility of root death to the lavender so I was dragging hoses. I'll go back out this weekend to ensure I watered sufficiently. If the weather stays warm and dry I'll most likely need to water these plants again before the ground freezes.I have another 1,000 lavender plants in one-gallon pots to be planted in the spring. I just have to keep them alive through the winter. If they die, it won't be due to the cold, it will be because they dried out during the winter. I watered each of these pots and will water them weekly until they are frozen solid. When the pots freeze, I'll tip them over on their side and cover them with a frost blanket material to keep them cold until spring. I could cover them with leaves to keep them cold but already have the fabric. I'll cover the pots of plants I have at home with leaves to keep them cold this winter.The pots have about an inch of space between the soil and the rim of the pot. This gave me plenty of space to fill with water. I watered them once and followed up with another watering to ensure the soil in the pot was thoroughly moistened. I like having adequate space at the top of the pot. If there was little space at the top of the pot to hold water I would have to water more than twice to get the soil wet. Some gardeners fill their pots up to the top with soil restricting their ability to properly water the pots.Whether you are watering outside pots you intend to over-winter or houseplants, it is important to water thoroughly when you do water. This does not mean watering so often you rot the roots off your plants but it is important to provide water to every inch of soil in the pot.I like to water a plant thoroughly once, allow the water to sink in, and then water again. I want water to run out of the holes at the bottom of the pot. The outside pots drained into the soil. I place trivets under my houseplants to keep the bottom of the pots above the water that drains out into the saucer. Watering like this ensures I flush out excess salts each time I water. Keeping the base of the pot above the water level in the saucer keeps the salty water from being sucked back into the pot. I also like to put my houseplants in the shower at least once a year and let tepid water dribble through the soil for 10 or 15 minutes to give the soil a good wash. I'll also turn on the shower for a minute or two to wash dust and mites off the leaves.The pots I'm over-wintering outside will be tipped over on their sides when the pots are frozen solid. This will help keep the roots in the bottom of the pot from rotting. Even though the soil will be frozen, there will be excess water at the bottom of the pot in the spring that could cause root rot. Many of the roots in potted plants are near the drainage holes in the bottom where they get adequate oxygen and water. By tipping the pots over, root rot should be less of a problem.When I was in Denver a few weeks ago I picked up rolls of Dewitt frost barrier. It won't be until sometime in January when I roll the fabric over the lavender in the field and over the pots. I'll pin down the edges of the fabric to keep it from blowing off the plants during the winter and will leave the fabric on until early spring. The whole purpose of keeping the soil frozen is to prevent the freezing and thawing of the soil during the winter. I don't want these plants to break dormancy too early in the spring. When woody plants go into the winter in a dry condition they tend to begin growth too early and suffer from freezing temperatures.Dr. Curtis E. Swift is a retired horticulture agent with the CSU Extension. Reach him at Curtis.Swift@alumni.colostate.edu or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.

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The Post Independent Updated Dec 6, 2012 02:37PM Published Dec 6, 2012 02:36PM Copyright 2012 The Post Independent. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.