Yuccas need to be watered deeply

With the 72 percent budget reductions being proposed for the Cooperative Extension by the University of Nevada, Reno, my weekly newsletter may have a tenuous future . This might include its circulation to readers, which currently comes from the university. You can always see pictures on my horticulture blog called Xtremehorticulture of the Desert, which can be found at http://xtremehorti
or following my column here in the newspaper. I put this site together, along with my column, to provide continuity and access to my advice in the event it was no longer supported by UNR.

Q: Any thoughts on what is going on with my yuccas? I think it is overwatering and would like to know how much water and how often it should be watered in the summer and winter. They are on drip.

A: The problem is that overwatering, underwatering and some other problems can cause the same physical appearance in plants. I would tend to agree with you that it is probably a watering problem, or a drainage problem where the water cannot freely drain from the roots. I do not think it is an insect or disease pest problem.

These look like possibly Spanish dagger, Spanish bayonet or recurved yucca. It is hard to tell from the picture and with that degree of damage. The leaves are heavily damaged with dieback, browning and discoloration. I will post it on my blogspot because I have had others send similar pictures to me.

Yuccas, depending on the species, can have some variability on where they are best suited for planting. Some yuccas must be watered more often or put into less stressful locations than others. Some are more cold hardy than others. It is a bit hard to generalize unless we know what yucca it might be.

Bottom line, these should be watered deeply, not with trickles of water from an emitter. So give them about 10 to 15 gallons each time you water. Then, depending on the species it might be as often as once a week in midsummer.

It might also be a location problem . If this is a hot spot in the yard with lots of reflected heat and light, this might be a microclimate problem. Some yuccas are native to the Southeastern U.S. and may be a bit sensitive to our soils and climate if not protected. Don’t assume they are necessarily all desert plants. They aren’t.

I don’t like it that it appears to be growing in rock mulch. It might be all right but its tolerance to heat and dryness will be affected by the soil conditions, which in turn affects plant health which in turn affects how plants can handle diseases, insect problems and environmental stresses. They are always a bit better off and more tolerant to stress if the soil is at least somewhat enriched.

Q: I’ve attached a couple of pictures of our poor pineapple guava plant. It did well until this year, but for some reason it is dying. The leaves are turning brown and dropping even though it gets plenty of water. It sits on the north side of a wall and next to the house, so it does get reflective heat. It has been fertilized and I have found no bugs or fungus. Can you shed any light on what is killing it?

A: It appears to be not getting enough water in combination with poor soils. Pineapple guava like to have a soil higher in organic matter than a soil covered in rock can provide. I know you think it has plenty of water but I would be giving this plant between 5-10 gallons of water per application three times a week in midsummer and about the same amount per application now but twice per week.

Rock mulches tend to allow the soil to mineralize (deplete the soil of organic matter and nutrients) in about three to five years after planting and applying rock mulch. I think you will see a dramatic improvement in the plant if you pull the rock mulch back about 3 feet from the tree trunk, put about 2 inches of compost around the base and cover that open spot with 4 inches of wood mulch. Then water with larger volumes.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by email at morrisr@unce.unr.edu.

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