Q & A Mailbag

By Judy Kunz, Colorado Master Gardener

Q. My iris plants have taken over my garden and aren’t blooming very much anymore. I give them a good amount of water and I’m wondering what type of fertilizer would help.

A. The main problem with your irises is probably not nutritional, but rather a case of overcrowding. When they are in a spot that receives enough sunlight and water, they tend to send out more leafy growth each year. This new growth shades out the rhizomes, the fleshy, horizontal growth just under the soil surface. It’s a good idea to dig the plants up, separate the rhizomes, and replant them with the rhizomes located just under the surface. This will rejuvenate the plants and give them enough space to receive adequate sunlight. Check here for more information on iris maintenance.

Q. Some of my tomatoes and peppers tend to get large brown spots on the bottom of the fruit. It doesn’t occur on all my plants and not all summer. How can I avoid this problem? Is it a disease and are the tomatoes OK to eat?

Blossom end rot (BER) tends to occur in tomatoes, peppers, squash and eggplant because of uneven calcium distribution in the plants. Some of the main causes can be drought stress, extreme temperature changes, uneven watering, excessive use of nitrogen fertilizer or mechanical damage to the root system. BER occurs on the bottom of the fruit and, unless it is severe, this portion can be cut off, leaving the remaining part of the tomato to be enjoyed. This is not a disease, but rather a management problem that can be solved by maintaining good cultural practices. More on blossom end rot.

Q. What exactly is “full sun” on the plant tags from the greenhouse? And what about a plant’s water needs?

Many greenhouse plants are grown at lower elevations and shipped to the Front Range area, and that means the tags on those plants may not be completely accurate regarding plant care. In this area, we have the advantage of being a mile closer to the sun than lower altitudes. This means that while “full sun” equals a minimum of eight hours at sea level, because the atmosphere is thinner and the sunlight is stronger here, we can get the same exposure for plants to complete the photosynthesis process with only about six hours in the sun.

Also, giving attention to a plant’s water needs is important for it to thrive. The soil at surface level may dry out sooner because of our dry air, so it is advisable to insert a finger several inches into the soil to determine the moisture level, watering accordingly. If a plant is drying out often, application of a weed-free mulch such as grass clippings, wood chips, or straw around the plant may be helpful.