Binetti: Helping young plants grow strong

On GardeningMay 21, 2014 

The third week of May means the honeymoon may be over and those sweet young plants you purchased are starting to show the effects of less than perfect growing conditions. Here are the most asked questions and some tips for figuring out what is wrong with your plants:

Q: I planted petunias in a large pot. Now I notice the lower leaves of the petunias are turning yellow. I think the plants look a bit wilted, but I water the pot every few days and keep the soil moist. It is a very large half whiskey barrel. Should I add more fertilizer? I mixed plant food into the soil when I added the petunias. — R.L., Kent

A: I suspect a drinking problem – as in too much water.

Here are the clues to this diagnosis. First, lower leaves turning yellow are a sign of root damage. Second, a plant that is over watered will start to look wilted as the roots rot from too much moisture and are unable to take up water. Third, you planted just a few plants in a large container – too much soil with too few plants in a container can hold an excess water especially when the plants are young and newly planted.

In our climate you might not need to water for weeks due to rain and cloudy weather, or you might not need to water every day even if the weather heats up.

Feel the potting soil and only add water when the top inch of soil is dry. Avoid a set schedule. I do not recommend more fertilizer – try to let the soil dry out even if it means placing an umbrella over the container or moving it under the eaves to protect from any more rain.

If your petunias continue to yellow and wilt, take them out and start over once the weather has warmed and the soil has dried up a bit.

Q: I love coleus and purchased twelve plants with large and colorful leaves to use as a contrast to my hosta in a new shade garden. I also added other shade-loving plants like lobelia, begonias and a lovely hydrangea. I improved the soil with compost and all the plants are doing great except for the coleus – the leaves have fallen off of most of these plants and some have black marks on the stems right at the soil level. Should I blame the nursery? The lobelia and begonias I purchased at this same place look great. — R., Email

A: Diagnosing your problem was easy – it is the classic case of the cold coleus. These colorful foliage plants don’t just hate a frost, they start shaking in their roots when the night temperatures dip to 40 degrees.

The other flowers you planted adjust to chilly nights but not coleus. The other clue to this cold case is that you added compost to the soil and there are black marks on the stems of the plants. Compost is great but it holds moisture and can encourage leaf and stem blight in plants like coleus that are super sensitive to cold damp conditions.

I would take tip cuttings of your surviving coleus by snipping out the top growth that might still be healthy and placing these cuttings into a glass of water indoors. If you see roots forming in a few weeks you can try again with coleus.

This time grow your coleus in containers of potting soil and keep them under cover and protected from spring rain storms and chilly nights.

Q: My lettuce has disappeared! A few days ago I was bringing in bowls of leaf lettuce and now all that is left are some bits of stem eaten off at soil level. Should I blame slugs? Should I replant? — S.C., Tacoma

A: Let’s not be too quick to think sluggish thoughts. I am suspicious because you did not mention trails of slime or any previous slug damage and it sounds like you enjoyed a healthy harvest just days before the disappearing act. Slugs would have found your lettuce stash weeks ago.

I suspect a rabbit, deer or other wildlife of ruining your salad days. You do have time to replant your lettuce from seed and still enjoy an early summer harvest.

This time, create a protective cage over the lettuce with hardware cloth or by fencing in the plot. If slugs are the thieves, you will need to protect the new seedlings immediately by setting out a pet- and human-safe slug bait like “Worry Free” or the “Sluggo” brand.

Rabbits can be discouraged by sprinkling red pepper flakes near the plants. Deer require a good fence or protective wire mesh cage over their favorite vegetables. There is one last suspect in this mystery. If you garden in an urban area, sometimes it is humans that sneak the fresh vegetables from gardens.

Take comfort in the fact that you were successful at growing lettuce and also at sharing your success with someone or something.

Meet Marianne

9 a.m. Saturday, Windmill Gardens. Learn how to grow landscapes and beautiful edible container gardens planed with food and flowers. Register at windmillgarden.com or call 253-863-5843.

Marianne Binetti has a degree in horticulture from Washington State University and is the author of several books. Reach her at binettigarden.com.

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