Difference Between Algerian and Dancy Mandarin Oranges

Q. I just bought a dwarf ‘Algerian’ and dwarf ‘Dancy’ mandarin orange. The Dancy is doing fine but the Algerian’s leaves are getting brown spots and falling. Is this a pest or disease? I don’t want it to spread!

'Algerian' mandarin (tangerine) with spots on its leaves. One person in Las Vegas growing citrus claims the secret to growing citrus here is soil drainage.

A. Our humidity is so low that I doubt it’s a disease problem. The reason for the difference in leaf brown spots could be its landscape location, adequate soil prep at the time of planting, or the genetics of the plant. The spots are most likely cultural, management; something you have done, or should be doing. Since it happened after transplanting, I’m guessing it has something to do with how it was planted, where it was planted or how the tree was irrigated.

Citrus Origin

            Both trees grow in the subtropics to tropics so make sure the tree was planted with a mixture of compost and soil in a planting hole about three feet wide and about 12 to 18 inches deep. The additions of organics in the soil should darken it. Cover this planting with a layer of woodchips to keep the wood chips rotting, full of organics and moist between irrigations. Make sure it is staked after planting in case there are strong winds.

Landscape Location

            If planting in full sun on the West or South side of a building and it’s showing signs of sun or heat stress, consider shading the tree’s canopy for the first year of growth. Shading doesn’t require shade cloth. It can be done with anything that provides some late afternoon shade. It is probably a good idea to shade the plants from the afternoon sun the first year.

Cultural

            Do not water trees daily except immediately after planting. Daily irrigations are meant only to settle the soil around the roots, not to give the tree a daily “sip” of water. Make sure it’s staked during its first season of growth. During the hot summer months, water as infrequently as every other day if two days of water is applied all at once.

            With a newly planted 5-gallon fruit tree, the tree should receive 4 to 6 gallons of water each time it’s watered. This water should be distributed through three , 2 gallon per hour emitters or four, 1 gallon per hour drip emitters under the canopy of the tree at about a foot from the trunk. As the tree gets larger over time, it needs more water applied over a lager area. Plan for it. Add additional drip emitters (not extra minutes) further from the trunk under the expanding canopy to give it this extra water. When the tree is fully grown at 20 to 25 feet, it should need about 30 gallons of water at each watering.

            Plant these trees at least three or four feet from hot walls and they should handle the reflected high temperatures okay if the soil is amended and they are watered before it gets hot. Fertilize the trees right after harvest with a citrus fertilizer. Prepare the soil with compost and make sure it has good drainage.

Dwarf Types

            Dwarf versions are grafted onto different rootstocks than the standard sized trees. This will impart a slightly different flavor to the fruit. The dwarf version of mandarin orange should get about 12 feet tall and 12 feet wide if unpruned. ‘Dancy’ mandarin oranges (sometimes called tangerines) are the most popular mandarin orange fruit in the world (sometimes called “cuties” in the supermarket). 'Algerian' mandarin oranges are noted for their winter cold hardiness.

What Do "Infrequent" and "Moderate" Mean?

Q. I’ve checked the internet and have some information from our state, but I still can’t compare the terms “infrequent" and "moderate”. Does “infrequent” mean once every two weeks?  Once a month? And what does “moderate” mean? 1 gallon per watering?

Root depth of plants has to do with their size, genetics and the kind of soil. The deepest roots are with large trees, from an arid climate and growing in a sandy soil.

A. I agree those terms are misleading. I think those terms are used by people who don’t understand the differences themselves or they would explain them. "Moderate" amounts of water refers to the amount of water a plant is given. "Infrequent" referst to the frequency of water or how often water is given. These are the two major concepts related to irrigation and are used to schedule any irrigation controller. It sounds like a topic for my audio podcast, Desert Horticulture.

Big Plants Need More Water

            Two concepts should be understood. Bigger plants have deeper roots. Deeper roots are encouraged with "infrequent" watering. This is about how often to give water. Plant roots extract water from the soil deeper and deeper as the soil at the surface gets drier and drier. The surface roots are the first to “suck up” water after an irrigation. The roots take water from the soil deeper and deeper as the soil gets progressively drier toward it’s surface. As we water plants “infrequently”, the roots extract water and grow into deeper and deeper layers of soil. Deep rooting of plants is the main reason good gardeners say, “Water plants deeply but infrequently.”

Get Away from Daily "Small Sips" of Water

            The major reason we do not give plants “tiny sips of water” daily is because this type of watering practice encourages plants to grow their roots more shallow. There is a second reason; tolerance to heat. Plants with deeper roots have a better chance of withstanding the heat of summer.

            “Moderate” amounts of water relates to the amount given to the plant. It usually means enough water to “wet the roots growing in the soil” and little or no more. We learned that the depth of plant roots depends on the size of the plant; bigger plants frequently have deeper roots than smaller plants. The depth of plant roots also varies with the genetics of the plant and the type of soil.

Water "Infrequently"

            The deepest roots are with those plants that are large, have the genetic potential to grow deep roots and grow on sandy soils. The shallowest roots are found on small plants that don’t have the genetic potential for deep roots and grow in a heavy clay soil.

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Ash Trees With Bark Lifting

Q. Our ash trees have “bark drop” as they got older. Should I worry that the light tan areas of bark are peeling in long sheets four feet long, and this bark seems to be coming away from the tree in small chunks?

Bark coming off or lifting from readers tree.

A. Worry only if your ash trees had the bottom branches recently removed and they were planted on the south or west sides of a building or wall. Try to leave the bottom limbs attached to the trunk as long as possible so the trunk is shaded by the limbs. Once the tree has gained some height and age, some of the lower branches can slowly be removed.

Beginning of ash sunburn after it was recently planted. The orangish-red color of the trunk or limbs is not normal for this tree and it was facing the sun. 

            Your job will be to discover if the trunk has been damaged either by the sun or by borers or both. Before you begin, establish which side of a wall or building the tree was planted on and make a mental note. South and west sides of walls and buildings are the hottest and most damaging.

Ash borers in the trunk of a young ash tree. Removing the loose bark will reveal their nasty work.

            Next remove any loose bark including those strips you mentioned. Use your hands first two pull off any loose bark. It won’t hurt the tree. Finally use a sharp and sterilized knife blade about 5 inches long to make the trimming cuts to undamaged wood just below the bark. The undamaged wood should be white or light green. The purpose is to hasten the healing either of the trunk or limbs and discover what did the damage.

Even though this is fruit tree it still demonstrates how to correct borer damage with a knife.

             It’s always a good idea to leave the lower living limbs for shading the trunk as long as possible. This shade helps protect trunk and limbs sunburn. Once these areas are sunburned, they will attract boring insects because these insects are attracted to damaged trees and shrubs. The sun burned areas are in the trunks and limbs where there is the most intense sunlight. This is usually the West or South facing sides or the tops of limbs and branches.

Texas Mountain Laurel Can Make a Medium High Landscape Screen

Q. I had Texas mountain laurel planted in my yard since 1998 and have not trimmed it at all; leaving it to look more shrub-like to act as a privacy screen, between the golf course and our pool.  It blooms profusely, leaving clusters of seed pods.  Would the tree benefit from having the pods removed, or is it best to leave them? Would I get more blooms if I trimmed off the pods?

Texas mountain laurel seed pods are objectionable to some and look fine to others. Prune them off if you dont like them. It will not hurt the plant.

A. Yes, the pods can be removed, and yes it makes more flowers when removed but the trigger for flowering is mostly in the early spring. Many people like the pods formed from the flowers as as well. The primary reason for removing the pods are looks; some people dont like their looks. Some do.

Texas mountain laurel with spring flowers.

            Texas mountain laurel is a Chihuahuan desert native plant so it can make a good heat tolerant 15 foot tall hedge after it is established. It would require about 2 to 4 feet of water applied under its canopy when mature. Remove only crossing branches to give it a full appearance and be careful about “limbing it up”. Let only knowledgeable landscapers prune this plant since it recovers slowly if mismanagement. Plant them no closer than about 8 feet apart. 

        They are relatively slow growing so it makes a privacy hedge that will be slow to fill empty spaces between them. Apply a fertilizer like 16-16-16 once in the early spring to get more and bigger blooms, prune it laterally so that it fills in these empty spaces faster.

What Does Light, Medium and Heavy Mean?

Q. I am confused by the terms, “light, medium, and heavy”?

Desert soils can be confusing. Even though this soil may be difficult to dig, it is a sandy loam soil; a mixture of sand silt and clay but the clay is not present in high enough amounts for it to be considered "a clay soil".

A. These terms usually describe soils, but could also be used to describe watering, such as a “light watering”. A light soil is a sandy soil. A medium soil is a soil has a mixture of sand, silt and clay but still drains water in a few hours to overnight. A heavy soil is a soil that is dominated by clay. It drains very poorly. These “heavy” clay or sticky soils hold water and don’t drain well. Oftentimes planting in these soils is a disaster for xeric plants because of the amount of clay and they hold water for a long time. 

This soil has a fair amount of clay in it. The type of clay makes it "expansive" or not. Expansive soils like this one are considered to have a higher than normal "shrink/swell potential" and cause problems when building or construction. Montmorillonite clay is an example of an expansive clay. Some clays are not as expansive as others.

To make a heavy soil “lighter”, about 90% more sand (v/v) is needed. The other option is to grow plants higher than the surrounding soil so their roots can “breathe”. Small plants need about a foot of soil higher (about 12 inches in diameter) than the surrounding soil. Large trees may need two or three feet tall mounds that are 6 to 10 feet in diameter.

What is a light watering?

            A “light” watering is an irrigation that wets the soil only 3 or 4 inches deep. It might be good for very small plants. This type of watering encourages lots of shallow roots to flourish and makes this plant less tolerant of hot summers. Shallow rooting oftentimes happens with “hose” watering; watering with a hose or a “breaker” at the end of a hose. 

Hose irrigation of corn in raised bed. Water not penetrating deep enough.

Hose watering raised beds and apparent adequate water until examined closely. Water was applied so quickly that it was only getting three or four inches deep but appearing wet, enough for shallow rooted crops but not deep enough for deeper rooted crops like corn. Drip irrigation is a better choice.

To water deeper (a.k.a. medium or moderate) requires watering the same soil about 10 to 20 minutes later but while it’s still wet. This drives the irrigation deeper in the soil and can wet the soil to a depth of 6 to 8 inches. A “deep” watering usually requires some sort of “moat” or “donut” around the plant to capture the water and cause it to go deeper. A third watering like this frequently doesn’t work but requires a “moat” or “donut” instead. Drip irrigation can release the water slowly, so it travels deeper. That’s one of the reasons why single emitter, nonadjustable drip irrigation is preferred in home landscapes and raised vegetable beds.

Giant Argentine Cactus Dying

Q. I have two Argentine giant cactus bought from a big box store last summer. I planted them in the garden soil after I amended it with sand, pumice, and vermiculite to improve drainage. Recently, I saw them with the tell-tale darkening associated with root rot. When the plants were new from the nursery, all branches were firmly set in the pot and upright. Is it usual for the limbs to feel flimsy?  Or, are the remaining limbs soon to rot and bend as well.

Giant Argentinian cactus from reader

A. Argentine giant cactus is a sprawling cactus that gets about 3 feet tall. You can read more about it by googling “Argentine giant cactus” and “ASU”. It’s possible that you might expect erect stems and get sprawling stems instead. Once they are out of their confining container and surrounded by open garden, they tend to sprawl.

Sometimes pumice is used as a soil ingredient for cacti and other succulents.

Root Rot            

It’s obvious to me that your cactus has root rot. It’s either from watering too often or poor drainage or both. In my experience adding too little sand, pumice and vermiculite can cause problems. Most of our soils benefit from additions of at least 80% sand. The vermiculite is another problem. Unlike perlite, it holds water and may make the problem worse. Bottom line, you have to add a lot of sand when you added and use perlite instead of vermiculite if you want to improve drainage.

What to do? 

If you want to improve drainage for cacti then plant them higher than the surrounding soil. These type of cacti require deep but in frequent irrigation. What I mean by that is when you water them make sure the water gets at least 18 inches deep and don’t water very often; maybe twice during the summer and only once during the winter.

Get a working soil moisture meter. 

Inexpensive soil moisture meters made in Asia are sometimes defective. Consider them to be disposable. Check it in the store to make sure it’s working before you buy it. Push the probe in the soil about 3 to 5 inches deep in several locations and water it when the soil moisture meter reads an average of two or three on the scale.

Use Your Eyes

            My observations of cacti tell me when I can water and I don’t use a meter. When their outside “skin” starts shriveling, it’s time to water. Just like any xeric plant, watering them causes them to grow. If you want cacti to grow, water them more often. If you don’t want them to grow much, then don’t water them as often. Always make sure that you’re not watering them so often that it causes root rot. Opuntia from the Sonoran desert I water every three to four weeks for fresh vegetable (nopales) and fruit (tuna).

Reduced Fruit Set Due to Spring Freezing Temperatures

Q. Did you see a reduced fruit set in plums, pluots, and pluerries this year or if it was just mine? I have 3- to 5-year-old trees and this year I just did not see many flowers at all. Not so much lack of pollination, but a lack of flowers. I fertilize with compost and try to keep an eye on how much growth I get each year. I want “fruit production”, not “wood production”.

Lightly squeezing the base of a flower AFTER the petals drop will tell you if there is a fruit present or not. The light squeeze will feel a small BB-sized fruit beginning to develop. Doing it this early tells you if the freeze killed the ovary before the fruit formed.

A. I look at fruit production from now forward to judge how much thinning (or none) should be started in about one or two weeks. Fruit removed should be about the size of your thumbnail. Sometimes late freezing weather removes fruit for me. Right now, early flowering peaches have fruit about the size of a large pea. A reduced number of flowers, however, usually means poor pruning practices. It’s best to be observant!

Youtube if fruit was killed by a late spring freeze.

            Fruit production varies where you live in the valley and in different microclimates. Some places in the valley (and landscapes) are warmer than other places. At The Orchard at Ahern, we have about 70 varieties of fruit trees producing fruit from late May through December. Our 25 – 30 varieties of peaches finish producing fruit toward the end of July and into the early parts of August. There are varieties that produce peaches in September or October but for me it’s no longer “peach season”. September through December is “apple or pear season”.

            The same holds true for apricots, apples, pears, plums but not citrus. Generally, early flowering fruit trees produce the earliest crops of fruit. These early flowering varieties are also the varieties most likely not to produce fruit because of late spring freezes. If you want to be sure to get early production of fruit, live where it’s less likely to freeze!

            About mid-March I observe the fruit remaining on earliest flowering varieties of peach, plum/pluot, and apricot as indicators for this year’s harvest. Right now, the earliest flowering peaches have fruit that are the size of a large pea. They also have dried up flowers and fruit dropping from the tree because of late spring freezing weather causing them to die.