I live in Phoenix Arizona and my Cypresses are approximately 13 years old and grow in clay soil. When it starts to get hot here around 90 degrees I notice the limbs start to sag. What could be causing this?
I would think that if those poor trees have been trying to grow in clay soil for that length of time, in heat and drought, they've done really well. What happens to clay soil in dry conditions is exactly what you would think; the holes where the trees are planted form a bowl.
Two things happen;
1: The 'bowl' will fill with water and depending on the length of time that the ground stays wet will drown the roots. Or:
2: The soil inside the bowl will dry out as the water capillary action draws the water out into the clay, depriving the the plants of water.
Either way, you'll have very sad plants.
Where these plants originate, you'll see them planted on quite steep hillsides, in volcanic (ie: very fast draining) soil.
A possible solution to your problem is to dig holes close by each plant, and replace the clay with a mixture of a small amount of the clay, lava rock, and possibly some kind of organic matter such as well rotted compost.
Each year, move a little bit over, and do the same thing, so that eventually, you've made larger areas of better soil that the roots can move into.
Disturbing trees of this age (quite likely, they're over 20 years old) will not be a good thing, but mediating the soil in small amounts over the next few years could save them.
Good luck, you've got a lot of work ahead of you!
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