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Ask the Ecologist:

by Belle Bergner

Q: I grow vegetables and herbs in pots on my deck and last year some of my herbs did not do as well as my tomatoes and peppers. I watered them all the same amount and kept the soil moist. Any idea what could have happened so that I don’t do the same thing again this year?

A: I’m afraid the answer might be right there in your question – you probably watered the herbs too much. This would be unusual for container gardens; typically, potted plants dry out much more quickly than people can remember to water them. It is important to know that most plants need their soil to dry out at least partially. Otherwise, roots may start to rot as soil micro-organisms out-compete the plant for nutrients or a mold or fungus may decay the roots.

Good drainage is essential. Check for the drainage hole(s) at the bottom of your pot before you fill it up with dirt. Make sure the drainage holes are unobstructed. You may want to add an inch of gravel to the bottom of large containers to aid in drainage – this also serves to add stability. Any pot with a drainage hole in the bottom needs a saucer underneath to help keep in moisture.

Your choice of container will affect your plants’ growth too. Clay or terra cotta pots dry out more quickly than plastic because they are more porous. You’ll have to water them more frequently than plastic, but in your case, this may be just what you need.

Please don’t start under-watering now that I’ve made you paranoid about watering too much! Just make sure the top of the soil is dry to the touch before you water each pot. Each plant will have different water uptake capabilities.

There may be some other things to consider in your case, or in our other readers’ cases: check off each item on the list below to be sure your container garden will be healthy this year.

• Make sure herbs and veggies get at least a few (3) hours of direct sunlight and some partial sun / shade. The more direct sun you get, the quicker the soil will dry out.

• Dark colored pots get hot and might make living conditions tough for the roots – especially if you get a lot of direct sun. Green is best.

• Make sure the container is big enough to allow root growth. Check the plant tag to get an idea of the plant’s mature size before planting. If in doubt, get a larger pot. A pot should also be heavy enough to resist wind.

• Good soil is essential. Fill the container with good quality potting soil (light, not too dense) up to an inch from the rim – any more soil will wash out when you water.

• Fertilize with either your compost, Milorganite™, a slow-release capsule fertilizer, or a dilute mixture of equal parts nitrogen – phosphorus – potassium (N-P-K). If you choose the latter, you’ll need to fertilize a few times during the season because potted plants leach nutrients faster than those planted in the ground. Too much fertilizer can burn the roots too.

If you continue to have problems, bring your plant to Kellner’s Greenhouses on Humboldt Avenue for Paulette’s special advice.

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Riverwest Currents online edition – May, 2007