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Annuals/Sunflowers stopped growing

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Expert: - 7/16/2009


Question

Red Sunflower
Since early June, I have planted numerous RED and WHITE Sunflower seeds.  They are outdoors in full sun in Phoenix, Arizona (temperature highs of 107-113F).  Many of them sprout, but they just grow a few inches high and stop growing (picture attached).  I water them daily.  I would appreciate knowing why they are hardly growing.  Last March, I planted YELLOW Sunflower seeds (temperature highs were only in the 80s) and they grew rapidly every day.  Could the temperature or the type of seed be a factor?  Thank you.

Answer
Alicia,
The hot temperatures may be causing this, but shallow, frequent watering might also contribute. You want to water these, and all plants, deeply less often. That means no hand watering - we get bored long before those root systems get a good, deep soaking. You want to water with a sprinkler, in the morning, leaving that sprinkler on for at least an hour and a half. Then wait until the soil is dry about four or five inches down before watering again. In 107 plus temperatures you'll probably have to water every other day, but when you water deeply the plants develop good, deep root systems and they can go longer between waterings. Also, remember that what happens below in the soil is reflected above. If a plant has a large, deep root system, you'll see large growth up above. If you have short, shallow roots, you'll have short growth above.

If you aren't hand watering, and are watering for at least an hour and a half, then you might conclude that the heat is the issue - perhaps this variety is more sensitive to high temps.

So what to do now? Water deeply every other day to start, transitioning to every third day after three weeks. One day after such a deep soaking, apply a liquid fertilizer mixed according to directions.  (Never fertilize a thirsty plant.)  And then hope for the best!

I hope this helps,
C.L.
    Questioner's Rating
    Rating(1-10)Knowledgeability = 10Clarity of Response = 10Politeness = 10
    CommentThe expert thoroughly answered my question and gave me some important gardening advice. Thanks.


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C.L. Fornari

Expertise

Annuals suggested for specific situations (sun, shade, windowboxes etc) New or unusual annuals are a particular interest of mine, and I grow many of these from seed. I am happy to help problem solve, answer questions about maintenance, and guide you to sources of unusual plants.

Experience

I am a garden writer/speaker/consultant and host of a weekly gardening radio program in the Northeast. I have been gardening all my life for my own pleasure, and started as a professional gardener and garden communicator 15 years ago. I work part-time at a garden center, selling and tending shrubs/trees/annuals/perennials...and doing some propagation and design work. I often think that all these professional activities serve to put a somewhat legitimate framework around a serious case of plant-lust.

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