Xtremehorticulture of the Desert: 07 March 2021

Thursday, March 11, 2021

How To Save Potting Soils for Future Use

Q. Should I be saving potting soils from seasonal purchase plants? I have been saving soils for years. Should the soil be thrown away at some po
int.

Garden Gourmet potting soil from Viragrow. It is made lighter in weight for containers or pots. Soil amendments like perlite, peat moss and even compost can be lighter in weight and hold water or nutrients.

A. Potting soils can be saved and reused for years. They can be valuable when added to our soils because of the “organics” they contain. These never go bad. But these “organics” don’t contain any plant nutrients and they can harbor diseases if used during their first few months after saving.

Rid this aggregated potting soil of any diseases it might contain by moistening and then placing it inside a clear plastic bag. Place this clear plastic bag full of potting soil in the summer sun for a few days. When it reaches a temperature of 180°F for 30 minutes or more, it will be sanitized of any diseases. Once sanitized, they are ready to reuse.

Rapid Summer Death of Shrubs - Collar Rot

Q. We have two 12-year-old Texas Sage shrubs concealing the street mailboxes. Within a month this past summer, they were dying back rapidly. The dieback spread over both plants. The irrigation hasn’t changed. Any idea what could be causing this?

Not readers plant. Showing collar rot. The top dies because its choked....rotten.

A. My explanation follows the KISS principle. Texas Sage, a Chihuahuan desert native, has roots that die if watered too often. If the main stem or trunk of this shrub stays wet, this could cause it to die. My guess this is a trunk/root disease caused by watering too often. This disease moves with irrigation water and can spread easily between nearby plants.

Put Emitters Close When First Planted

When first planted, the drip emitters must be close to the plant. I like to put them up to about 12 inches during the first year. They should be moved, and more drip emitters added, as the plant gets larger in the second or third year. They are moved to about 12 to 18 inches away from the trunk at this time. This practice does not change the irrigation frequency but changes how much water is applied and where it is applied. A larger area under the plant is watered to compensate for its increased size.

Move the drip emitters away from the trunk or main stem to a distance of 12 to 18 inches from its trunk. This should be done when the shrub is 2 to 4 years in the ground. At the same time, add more drip emitters and redistribute the emitters so that they irrigate half the area under the enlarged plant canopy. This gives the plant more water, distributes the water to a larger area because it’s larger and reduces the chance of trunk/root diseases of susceptible plants.

Mistakes Made When Planting in Desert Soils

The major mistakes made when planting are not making the planting hole wide enough, digging the hole extra deep when it’s not needed, planting too deeply, and watering the plants too often after planting.

The amount of "organics" in a soil can be "eyeballed" in many of our soils by its color. When a soil is darker in color, it means it has more "organics" in it. The Mojave Desert soils in Las Vegas have generally have no organics in them at all. This is why we add organics to the soil, oftentimes in the form of compost, to raise the level or its content. This is Garden Soil Mix from Viragrow and used for planting.

I like deals

Buying a large tree in a box and getting it planted for free is a good deal! Just have it done right. Beware. Numerous people have complained the “planting crews” dug the hole only wide enough to fit the box in the planting hole. After that a little bit of mulch is mixed with the soil, watered in, and called good. That’s no deal. The tree will decline and maybe die in a couple of years because of these poor planting techniques.

Yellowing leaves like in this bottlebrush can be a sign that the organics in the soil is running out due to its mineralization in a few years by rock mulch. Some plants dont like rock mulch but want a soil that has at least 2% organics in the soil. This soil under the rock probably has less than 1%.

Planting Right

If these deals are too good to pass up, then make sure the planting hole is at least three times the width of the box. Pay planting crews extra to do it the right way if you must. The hole doesn’t have to be dug extra deep, but it should be dug wide. It’s okay to use the soil taken from the hole for planting, but first mix it with about one third by volume of compost. If a normal compost is used, make sure to mix in some fertilizer with the soil used for the planting hole. “Rich” composts don’t need extra fertilizer in the soil mix.

Use this soil mixture for filling the planting hole around the rootball and then water it in with lots of water. Water it like this for two days in a row. Make sure the tree is watered thoroughly at planting time., To force the water deep in the planting hole, construct a “well” or “moat” 4 inches tall just above the planting hole and fill it with water.

Deep Holes - No, No, No

The planting holes shouldn’t be super deep. (unless there is a problem with drainage which is more rare than you might think). If a hole dug in the soil drains water overnight, there is no drainage problem. However, if the water is still in this hole by morning, then there is a drainage problem and other planting methods are needed. But poor drainage is not frequent in most of our landscapes.

The soil around the tree in the box or container should be “milk chocolate” in color when wet and the same level as the rest of the landscape soil when everything is finished. The tree should not be below or above the surrounding soil when finished. Make sure the soil is wet when planting.

Why Stake

Staking trees and shrubs can be very important in getting the roots established during the first year. The stakes that come with 5 and 15-gallon plants are usually good enough to reuse if cut free from the plant and pounded into the solid soil at the bottom of the planting hole so the plant roots can’t move. The purpose of staking is to keep the plant roots from moving, not necessarily the top of the plant. The top of the plant should be free to move in the wind.

Watering Shrubs Daily a Mistake. Why?

Q. I live in a climate very similar to Las Vegas; USDA Zone 8B. I planted a 1-gallon Texas ranger shrub two weeks ago in sandy/stony soil, watered them with about 2 gallons daily for 10 days. After, I put a 1-inch deep, bark mulch on the soil surface. Now, three weeks later, the leaves are yellow, brittle and crunchy on the lower stems with curling leaves on the top. I think I overwatered, but I’m not sure.

Honeysuckle crown or collar rot. A disease of plants that are watered too often.

A. Yes, sounds like they were watered too often and now probably “root dead”. Watering too often has caused the leaves to yellow, brown, and get crunchy. After the initial watering, let the soil drain water and give the plant roots air.

The plant roots drowned because the plant was continuously watered. Watering the plant with 2 gallons is about the right amount after planting. It could even be more than that. But after that, schedule the irrigations to skip at least one day so the water drains from the soil in the roots can “breathe”.

This time of year in early spring, probably once or twice a week watering is enough, even for a sandy/rocky soil! The soil around the roots was amended so it will hold water. The bark mulch on top of the soil gives you about a day extra between irrigations.

The bad news is that the soil surrounding the overwatered dead roots is probably “contaminated” with root disease problems. It could be replaced I suppose but I suggest digging a new hole for planting, at least 2 or 3 feet away from the old, contaminated hole.

Dig the hole 2 to 3 feet in diameter for a 1-gallon plant. It doesn’t have to be deep, but wide. Next, mix the soil taken from the hole with about one third compost. Wait till the last minute and finally remove the plant from the container. To do this, turn the container over and let the plant slide onto your hand. Lower the plant into the hole, holding it by its rootball, and place it so it’s resting at the bottom of the hole.

As you are pushing this mixed soil back into the planting hole, everything is wet. Make this planting soil a “slurry” by adding water slowly to the whole with a hose so this “slurry” flows and fills all the gaps around the rootball. You should see air bubbles surfacing from this slurry. Build a moat, 2 foot wide, around the plant to force excess water down and not run off the soil surface. Fill this moat with water. Do this twice. No more than twice.

If the plant came with a nursery stake, push it into the wet, solid soil at the bottom of the hole next to the plant and re-tie the plant to the stake with stretchable, green nursery tape. This immobilizes the plant until the roots have anchored it into the soil. Remove this stake at the end of the growing season.

If you buy 5-gallon plants, use around five gallons of water when irrigating with the timer. If you buy 15-gallon plants, plan on around 15 gallons of applied water when irrigating. What killed the plants is watering too often, not the amount applied.

Apple -- Crown and Collar Rot

From http://plant-disease.ippc.orst.edu/disease.cfm?RecordID=40

Vegetables like beans can have crown rot (collar rot) when planted in cold soils. Different varieties of beans will show different tolerances to cold soils and collar rot development.

Cause: Phytophthora cactorum and other species, a soilborne fungus-like microorganism. Crown rot is a disease of the rootstock portion of the tree; collar rot is a disease of the scion portion. Both are serious diseases of apple and other orchard trees in British Columbia, Washington, and Idaho, and have become a problem in Oregon orchards with clonal rootstocks, principally Malling Merton 106. Crabapple can also be infected.

The fungus survives primarily as oospores in soil, organic debris, or infected tissues. Oospores produce a swimming spore stage (zoospores) when soils are at or near saturation. Zoospores swim to and infect roots. Movement within roots to the root crown is greatest between pink bud and shoot elongation.

Apple crown rot in Lebanon

Symptoms: In early fall, an affected tree shows bronzing, purpling, or yellowing foliage of one or more limbs, accompanied by bark reddening. There is a reduction in the size of leaves and terminal growth. Examination at the root crown or collar after scraping away the soil reveals dead bark. The cambium will be orange-brown to red-brown, eventually becoming dark brown instead of white. A distinct margin may separate healthy from infected tissues. In many cases, the tree may be completely girdled before its condition is noticed. Fire blight symptoms may be similar when confined to the rootstock.

'Antonovka', 'McIntosh', and 'Wealthy' apple seedlings and M9 clonal rootstocks have shown high resistance to collar rot. Moderately resistant: MM111, M2, M7, M26, 'Golden Delicious', 'Delicious', and 'Rome Beauty'. Susceptible: MM104 and MM106.A

Cultural control:

Plant on a raised bed to help keep water away from trunks.
Avoid overirrigation.
During summer, examine root crowns of trees for collar rot and scrape off diseased tissues. Leave root crowns exposed to the air until late fall.
Avoid wounding root crowns. If a wound is made, keep it uncovered and open to the air for the remainder of the season.

Chemical control: Apply before symptoms appear, especially in orchards favorable for disease development. No chemical will revitalize trees showing moderate to severe crown rot symptoms. Although resistance has not been reported, alternate materials so resistant fungi do not develop quickly.

Agri-Fos at 1.25 to 2.5 qt/A. Do not combine with a copper-spray program for control of other diseases. 4-hour reentry.
Aliette WDG at 2.5 to 5 lb/A. Spray foliage to run off. Follow manufacturer's directions for timing of spray. Do not apply within 14 days of harvest or more than 20 lb/A per season. Do not combine with a copper spray program for control of other diseases. Phytotoxicity may result if applied within 1 week of a copper spray. 12-hr reentry.
Fixed copper products. Use 4 gal solution as a drench on the lower trunk of each tree in early spring or after harvest. Do not use if soil pH is below 5.5. Not considered organic since application is to the soil.

Champ Formula 2 at 2.75 pints/100 gal water. 24-hr reentry.
Copper-Count-N at 4 qt/100 gal water. 12-hr reentry.
Cuprofix Disperss at 5 lb/100 gal water. 24-hr reentry.
Kocide DF at 4 lb/100 gal water. 48-hr reentry.
Nordox 75 WG at 2.5 lb/100 gal water. 24-hr reentry.

Fosphite at 1 to 3 quarts/A. Do not use copper products within 20 days of treatment and do not use spray adjuvants. May also be injected into trunk. 4-hr reentry.
Phostrol at 2.5 to 5 pt/A. 4-hr reentry.
Ridomil Gold SL at 0.5 pint/100 gal water. Apply diluted mixture (based on trunk size measured at 12 inches above the soil line) around each tree trunk. Apply once at planting or in spring before growth starts. Apply again in fall after harvest. 48-hr reentry.

References:
Jones, A.L. and H.S. Aldwinkle. 1990. Compendium of Apple and Pear Diseases. 1990. St. Paul, MN: APS Press.

Content edited by: Jay W. Pscheidt on January 1, 2008