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Wednesday, April 3, 2013

Xtremehorticulture of the Desert Exceeds 20,000 Hits per Month

I am excited that my blog now consistently exceeds 20,000 hits or visitors each month. My blog is my way of paying back to southern Nevada residents for all their support over the last 30 years in my tenure with the University of Nevada. I have learned alot about horticulture over the years teaching and conducting research in southern Nevada. It is a shame to retire and have that information retire with me.

I hope you can use the information I am providing and, in the process, make you better gardeners and horticulturists.

I have returned from my assignment in Northern Afghanistan and I am excited to share some of what I learned there. I was concerned sharing much at that time due to security issues. Any pictures of individuals who worked with me there must have their faces blurred for obvious security reasons. Please bear with me when I share these experiences. Northern Afghanistan's climate is very similar to southern Nevada and their crops and planting schedules were nearly identical to ours. So stay tuned. More to come.

Tuesday, April 2, 2013

Saguaro Leaning and How to Correct It

Q. I have a saguaro cactus with three big arms growing from it leaning toward the west. On the east is my house and shading the cactus from the morning sun. I also have been watering on the house side of the saguaro, the up slope side, and letting the water run downhill into the roots.  I water about 3 or 4 times a year and water very slowly.

Do you have any suggestions about either stopping the continued leaning or how to straighten the cactus to upright?  Those two large saguaros have been in my yard for 17 years.

Saguaro leaning due to shade from the house most likely
A. These Sonoran desert monsters are top heavy. The root system of the saguaro is fairly shallow but expansive. This extensive but shallow root system can give this top-heavy cactus quite a bit of support under native desert conditions. But they have been known to blow over in high winds.

These cacti, like most, are opportunists and take shallow water from the soil before it evaporates or taken by neighboring plants. Most of the roots away from the trunk can be found at depths less than 12 inches. Watering deeply around these plants is probably a waste of water.

We put these plants in artificial desert landscapes and put them on drip emitters or run water close to the trunk. This can lead to a very small but dense root system close to the trunk. The roots don’t have to grow far from the trunk for water and so doesn’t help to stabilize the plant as the top gets bigger.

Saguaro normally does not need to be staked when transplanted but here is one method that protects the trunk
Your cactus could be leaning either because of the shade from the house or it might be leaning due to poor root support or both. If it is leaning and there is danger it will fall over then you will have to support it.

In the meantime, we create a more expansive root system by placing enough other desert plants close to this plant so that the irrigations from these other plants can help the saguaro extend its root system further from the trunk.

We could sprinkle irrigate the area around the saguaro, simulating desert rainfall. But sprinkler irrigation can lead to weed invasion in the landscape and weed control problems.

From the pictures you sent, obviously your watering regime has given your saguaro some good growth but it sounds like the water is concentrated close to the trunk. I will post the pictures of your saguaro on my blog for others to see.

Another possibility that could contribute to the leaning is how it was planted. If a hole was dug just large enough for the transplanted roots, and the soil was not conditioned properly, then this will encourage the plant to grow roots close to the trunk as well.

All cacti grow better in amended soils than in straight desert soils or sand. Always amend soils for cacti at planting time.

What can you do now? If the plant is leaning due to the house there is not much you can do. To give it better support put irrigation water at greater distances from the plant and use shallower irrigations.

Like I said, giving saguaro deep watering is not going to help but getting its roots to grow wider might. If the soil is not loosened, it is best to loosen the soil surrounding the plant where you are watering to encourage growth at distances that will support top growth.

Keep the Birds Out of Ornamental Grape Vines by Removing Flower Clusters

Q. I bought a house last December that has two large grape vines growing over a pergola that covers a hot tub. Last summer when the vines were producing grapes, the birds were unbearable. I know I could cover the whole thing to keep the birds out but it would ruin the aesthetic and make access to the hot tub difficult. Is there something I can to keep the beauty of the vine without it producing any grapes?
This is a grape spur that has been pruned for producing good quality grapes. The top stem is reddish brown. At
the base of the reddish growth is greyish-brown. The reddish brown growth will produce grapes because it grew
last year. The greyish brown growth is older and will ot produce grapes. If all the reddish brown growth is removed
from the vine, the vine will not produce any fruit
A. Yes you can. It is a fairly easy solution. In the winter months prune out all the new growth. You can see it because it is a different color than the greyer oldish growth. Grapes only flower on the wood that grew last year.

            Or it should be flowering now or very soon (late March). As you see these flower clusters on the vine, pull them off.

These are unopened flowers of grape. They come around late March to early April in southern Nevada. The come
from the reddish wood produced last year. Either remove all the reddish wood during the winter or early spring or
wait until these flowers come out and remove these clusters. They snap off easily so you could probably knock them
off with a broom if you don't want fruit

When and How to Prune and Fertilize a Cassia

Q. My cassia is full of beautiful yellow blooms. First year this two year old plant has done this. When do I trim it back and how far?  Type of fertilizer will it need?  

The base of cassia has several strong stems coming from the base. Choose one or two of these strong stems and remove
then at the base. Let it regrow from the base to rejuvinate it and let the leaves fill in from top to bottom from the
strong young basal growth.
A. Shrubs or other plants should be pruned soon after they flower. In spring flowering plants the flowers are produced during the late summer and fall months. Some finish maturing in the spring before they flower.

But regardless, if these spring flowering shrubs are winter pruned with a hedge shears it will remove the spring flowers. If shrubs are pruned properly and not pruned with a hedge shears they then can be winter pruned. Hedge shears should be reserved for nonflowering hedges.

Reach down inside the canopy, or from the outside, cut with a sharp and cleaned pruning shears about one inch above the
surface of the soil and make your cut. Pick stems that are the largest or too close together.
Pruning should be done with a few well-placed cuts deep inside the canopy to remove sections of the plant which are crowded, too tall or too wide. Cuts are made where two stems join together, removing the offensive stem.

This results in a general thinning of the shrub removing larger diameter wood. By removing larger diameter wood, this “renews” the shrub and helps keep it young. I hope this helps.

Center of Cassia Bush Died. What to Do?

Q. I have a cassia at the corner of my house to block the street view of my air conditioning unit.  The whole center section visible from the street has died.  I'm beginning to cut out the dead limbs. I check the cuts but am not seeing any green at the bark.  Is there a chance that partially cut back limbs might still produce new growth?  Or should I cut back to the main trunk?  With no center section it looks ugly. Can I hope the living branches will fill in eventually?  Dig it out and replant with a new one?

One of the cassias and what it should look like with proper care as it is getting at the Las Springs Preserve
A. Yes it is possible you had some winter kill but doesn’t sound like winter kill. Winter kill is most common on new growth, such as the tips of branches, if temperatures are just below their tolerance. If temperatures a considerably below their tolerance, then you will see death also in the older, larger diameter wood.

This is what a cassia will look like armed with hedge shears, improper watering and lack of
fertilizer 5 years after planting.
It is odd if it is just damaging the interior wood and leaving other parts of the plant alone. Another possibility is root rot if it is watered too often or the area is flooded. This should be fairly easy to determine by pulling the top of the plant toward you and looking at the base of the plant.

In cases of root rot, trees and shrubs the plant will not be securely anchored in the soil. When you pull on it the base will move around and not be firmly anchored in the soil.

In healthy plants that are not winter damaged you should be able to scrape the soft outer bark with your fingernail and see green beneath it. This is not easy to see in all plants. But at least the inner bark should be cream colored or white.

So I would not cut anything back at this time. If there is winter damage then the killing temperatures already “pruned” it back. If the plant or plant parts are alive they will show you where to cut after new growth emerges. When it emerges, cut a few inches below the dead part of the limb and into the strong growth, just above a bud or at a crotch (where two stems come together).

If you don’t see any new growth by mid-April, then it is dead. Whether to remove it or not is really a subjective call and not one I can direct. It is your call. With an established root system it should grow back very rapidly and will fill in the spots where there is strong sunlight.