Soil moisture sensors not always accurate
Q. You recently gave me advice on planting pancake myrtle. I dug the planting hole as deep as the container and five times as wide, but didn’t do a water percolation test to make sure the planting hole was draining water. I backfilled the hole with a 50/50 mixture of the existing soil and a rich Viragrow compost. However, a soil sensor consistently recorded a “10” (very wet) even for weeks after just one watering.
A. Be careful when purchasing a soil moisture sensor. Sometimes they don’t always work.
Before you buy it, get your hand wet and make sure the sensor on the tip is working. A “wet hand” tightly wrapped around the tip should move the needle to or at least near the “10” you mentioned. When the sensor is in the open air and dry, the needle should point to “0” or approach it. Buy only humidity sensors that are working properly.
Pancake myrtles come from the eastern and cold regions of Asia, including northern and central China, Korea, and Japan. When it was introduced to England in the mid-1800s, it did not flower profusely because it was not warm enough. This tree, much like the native Carolina laurel, really likes the warmth of the southern and southeastern United States for flowering.
The reasons it was introduced to the desert is that it likes heat, is quite drought tolerant, and tolerates a wide range of soil alkalinity. Crepe myrtle does not like soils without compost, very intense western and southern slopes without afternoon shade and the low humidity of our desert. In our climates, this tree likes northern and eastern exposure, and regularly amended soils.
If the soil does not drain water very well, raise the soil where you are planting to a height of 12 inches and 4 feet in diameter. Don’t plant at the bottom of a ditch unless it likes boggy soil. The soil mound allows the roots of the plant to grow by providing water drainage to the lower soil surrounding the tree.
Q. I am concerned about the appearance of my jasmine vine and rose bushes in my garden. I fed everything with 1 cup of Epsom salts two months ago and fed rose bushes with rose food last month and this month. I watered abundantly before and after the meal. My garden has a drip system that waters for 30 minutes three times a week.
A. It is true that some rosarians like to give Epsom salts to their roses, but that does not excuse the condition of your plants. Epsom salts provide the soil with magnesium in the form of sulfate. Typically, in our alkaline soils, the compost contains enough magnesium to enrich the soil without using Epsom salts. Make sure the soil used in the ridging drains the water.
I don’t know where your trees grow, but the preferred landscape exposure for both plants is the east and north sides of a house or wall. Jasmine and roses like soil amended with compost. About half an inch of compost sprinkled on the ground each year is enough to keep these plants healthy and growing at their best.
Just like us, when these plants are healthy, they tolerate heat and cold better. When these plants aren’t healthy, they don’t tolerate these temperature extremes as much. If the soil is covered with rock and not improved, they will struggle a few years after planting.
What to do? If the soil is amended with compost at the time of planting and the surrounding soil is covered with wood chips, then fertilizer is usually sufficient. Adding compost sprinkled on the soil surface once a year adds a lot of plant nutrients to the soil that is lacking as the rock breaks down. Don’t overdo it and keep rocks or wood chips at least 6 inches from the trunk of young plants. Both plants will benefit from annual applications of EDDHA iron chelate in early spring.
Q. Please see the picture of this unhealthy looking palm tree.
A. The photo you sent is not a palm tree although it is called a “sago palm”. This plant is also called a cycad. Let’s agree to call it a “cycad.”
These plants are native to China and Japan and are now cultivated in nurseries around the world. They can handle a lot of difficult locations and poor soils, but they look great when growing in filtered shade and in sandy but enriched soils.
If I had to grow them in a desert landscape, I would place them on the east or north sides of a house or wall, spacing them about 3 feet and 3 feet from walls and buildings. Keeping in mind that they “like” filtered light, I would find a place where sunlight is intermittent. They give a tropical and jungle look to a landscape and should be used where there are a lot of other plants growing.
The soil should be enriched and covered with 3 to 4 inches of wood chip or wood chip mulch and need 5 to 10 gallons of water each time they are irrigated. They are “mesic” in their use of water and should not be watered with the same valve that is used for desert plants like cacti, saguaro, Joshua trees, and ocotillo.
The worst way to grow this plant is on the west or south side with reflected heat, grown in unimproved soils covered with rock and watered like a desert plant. If you can check one of them, your cycad is or will be in trouble.
Q. A few years ago I was fortunate enough to grow a Japanese dwarf pomegranate from a 6 inch cutting. He is now over 5 feet tall. What is a well-cut grenade supposed to look like?
A. The Japanese dwarf pomegranate is an ornamental shrub. It is not appreciated for its fruit. The size is like any other ornamental shrub. Pruning is done once flowering is complete. I assume your ornamental pomegranate flowers for most of the year, so they should be pruned in the winter after the leaves have fallen, just like pruning the pomegranates which are used for their fruit.
The rule of five to six stems that we use for pruning fruit pomegranates is not important if we are using it as an ornamental. This means that you can leave as many stems as you want. As the shrub grows, remove a quarter to a third of the larger stems by pruning them close to the ground. You should remove three or four of the larger stems every two to three years. Pomegranates grown for their fruit are pruned every year during the winter.
Q. Can I use burlap for shade cloth?
A. Do not use burlap as a solid piece in place of shade cloth for permanent shade. It’s good for creating permanent shade for people or pets, but not for plants. Pay attention to the amount of heat it traps if it is located too close to humans and animals. Plants are green and need sunlight for photosynthesis. Usually about 60 percent to 70 percent of sunlight. Humans and animals don’t need it.
Instead, use a shade cloth. It comes in different shade percentages ranging from around 30 percent to 100 percent. The shade fabric for plants ranges from 20 percent to about 50 percent shade. Plants that flower and produce fruit like tomatoes, peppers, and eggplants need more light than leafy plants: 20 to 40 percent shade. More shade than that interferes with flowering and fruiting.
Plants that only grow leaves such as lettuce, spinach, Swiss chard, and green vegetables can withstand up to about 50 percent shade. After that, they grow poorly because it is too dark.
Most of the burlap I’ve seen produce a lot more shade than that and wouldn’t be a good choice for growing plants.
You can create 50 percent shade from 1-by-2 lumber by omitting any other piece of lumber. These are called tower houses. Likewise, 30 to 40 percent shade can be done the same way, but removing two and leaving every third 1 by 2.
Bob Morris is a horticultural expert and Professor Emeritus at the University of Nevada in Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send your questions to [email protected]