moisture and water... newbie question

13 years ago

I've inherited a large patch of roses in a slightly raised bed (about 4 inches). They're mostly hybrid teas and floribundas.

They're in a fairly rich soil (a compost based mixture meant for growing vegetables). Underneath this is fill dirt from when the house was built and then gumbo clay. A variably thick layer of red-dyed wood mulch (1-2 inches) is on top. None of these layers are very distinct. I "inherited" this flowerbed after significant early spring regrowth had occurred, but I did try to amend the soil with sulfur, as well as attempt to head off fungal diseases with sulfur/copper powder.

My question is this - If the soil underneath the mulch is is clearly moist, and this moisture increases as I go deeper until I hit wet gumbo clay, am I correct to withhold irrigation even in very hot weather(mid 80s to 90s). It will obviously get even hotter as we move into summer.

I ask because small parts of some bushes appear dry or even crinkled... and that makes me want to water them. But I've now realized that's probably counterproductive (I dig a little hole each time to convince myself). We're in the midst of 2-3 month drought, so rain isn't a variable. The last time I watered the roses was at least a week and a half ago. I'm fairly confident this isn't a specific infectious disease or pest.

Also, I see some yellow interveinal chlorosis and slight leaf narrowing on new growth of certain bushes (but not all of them). I thought this might be iron deficiency caused by anoxic conditions in the root zone.

Growth wise, the roses are very large/vigorous, with plenty of blooms. The ones with interveinal chlorosis are less vigorous. There is some sporadic blackspot on the lower parts of every bush, but it is being well controlled by regular removal of infected tissue and the Bayer 3-in-1 Systemic product.

Right now I've treated with an iron chelate foliar spray, gentle aeration with a hand cultivator, and forcing myself to not water them :P

Thanks for reading this long post, and for any advice!

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Comments (5)

michaelg
13 years ago
One thing you should know is that, even in well-drained soil, most of the feeder roots are in the top 6 inches. This layer needs to be consistently moist if the roses are to grow and bloom continuously. Another is that the gardener's judgement of "moist" encompasses a range that may include not-quite-moist-enough.

As long as they grow continuously, you are OK. New growth should start at the upper leaf axils within 7-9 days of deadheading or pruning. Almost all new shoots should flower as opposed to going "blind." So basically you need to judge water by how the plants are doing.

10 days without water in hot weather seems like a long time, though. Most gardeners who irrigate for maximum growth do so at least once a week. If you have a non-drainable layer a foot or so down, it may be better to water your shallow soil only 1/2" inch at a time but at closer intervals (perhaps twice a week).

As you suggest, saturated soil can cause iron-deficiency chlorosis, but you ought to check the pH as well. Roses do best at pH 6-6.8. Narrowing of new leaves could suggest some other trace deficiency such as zinc.

I wouldn't recommend cultivating rose beds. The feeder roots come right up to the mulch boundary.
vuwugarden
13 years ago
"If you have a non-drainable layer a foot or so down, it may be better to water your shallow soil only 1/2" inch at a time but at closer intervals (perhaps twice a week)."

Great advice! I will follow these suggestions for my own garden. Thanks for sharing your knowledge!

Audrey
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michaelg
13 years ago
Audrey, I have shallow-soil areas in my terraced garden, so I water that way and it has worked fine. Same goes for very fast-draining, sandy soils.
greentiger87
Original Author
13 years ago
Thanks for the advice, it makes a lot of sense. However, I'm now realizing that the curled/distorted leaves I'm seeing are probably chilli thrips :( The rosebed is FULL of blooms right now, but all the new foliage is really damaged. I'll just have to enjoy it while I can, hope for Spinosad and the Houston heat to save them.

The minor chlorosis seems to already be responding to the foliar spray (is that even possible)? I also worked in some iron chelate and sulfur.

Thanks again.. it always amazes me how the internet lets you pick the brains of people who have dedicated large parts of their lives to something you're new at.. and they give information away freely. It's much, much appreciated.
michaelg
13 years ago
Greentiger, you are welcome. Come back any time. Very sorry to hear you may have to deal with chilli thrips.

moisture and water... newbie question

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moisture and water... newbie question

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