Nitrogen deficiency

Dear Ed,
I have ten plants in my garden. They are all in enriched potting soil in six inch pots and are about a foot tall and bushy. This week the leaves on the bottom of the plants started turning yellow and it is progressing. Should the plants be doing this?

Burnaby, BC

The plants are suffering from a nitrogen deficiency and may be in containers that are too small. They should be fertilized with a high nitrogen (N) fertilizer. Check to see if the roots are girding the container. If they are, they can be transplanted into 10-12 inch diameter containers.

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