Proper pruning, thinning, irrigation increases fruit size

Q: Peaches from my dwarf peach tree were very small again last year. This is the third year the fruit developed into a small size. We fertilize them twice a year with vegetable spikes and our in-ground system fertilizer system has Dr. Benson’s Natural Mix added five times per year. Any suggestions?

A: This problem does not have anything to do with fertilizers — either the kind of fertilizer or the amount. You didn’t mention the management practices you are applying to this tree, but three management practices are extremely important when increasing the size of fruit. These are pruning, thinning and irrigation. Fertilizers need to be applied, but a single application of fertilizer in early spring is all that’s needed for good-sized fruit.

■ Pruning. Pruning genetic dwarf or miniature peaches focuses on removing some of last year’s growth at the ends of branches. There is a cluster of new shoots, much like fingers on a hand poised to grab something, where most of this pruning occurs.

These clusters of new shoots are thinned or removed, leaving only one or two “fingers” instead of five or six. This is a very important step because all of these fingers will have flowers and future fruit. As we will see later, having too much fruit on the tree results in small fruit.

■ Thinning. A few weeks later, when the fruit is about the size of a marble, excessive numbers of fruit must be removed along the branches. This is called thinning. The remaining fruit should be about 4 to 6 inches apart.

Thinning fruit early when it is small reduces the number of fruit the tree must feed with its leaves and roots. The remaining fruit gets larger if the tree is watered regularly during fruit production.

■ Irrigation. For fruit to get larger, water must be available to the tree. This water is picked up by the roots and sent to new growth, leaves and fruit. The fruit uses this water from the roots to expand and get bigger. Limited or not enough water during times when the fruit is getting bigger equals smaller fruit.

This does not mean you should water every day, but do not let the soil around the roots get dry. If you’re not sure when to water, use an inexpensive soil moisture meter (like the kind used for houseplants) to tell you when water should be applied to the tree. Stick the soil moisture sensor in three different locations around the tree and if the average reading is six or lower, it is time to irrigate.

Be sure the tree has enough water to moisten the soil all the way around the canopy and about 18 inches deep. Only in very rare circumstances should a fruit tree be watered daily. In the heat of the summer, give these trees at least one day without water between irrigations. This gives the roots a chance to breathe.

I encourage people to use organic mulch, such as woodchips, 4 to 6 inches deep around their fruit trees. On new trees, keep it away from the trunk at least 6 inches so the trunk doesn’t rot.

Q: Any ideas about why my 20-year-old star jasmine leaves are turning red, then yellow? Could this be from freezing temperatures as you described in your blog? It’s a spectacular vine and I’m terrified of losing it.

A: Judging from the picture you sent, the vine looks old, tired and not all that healthy. I don’t think it was due to cold weather because it can handle temperatures as low as 15 degrees F.

Unfortunately, star jasmine is frequently used as a groundcover or vine in desert landscapes where the soil is covered in rock. This causes future problems with this plant, such as poor growth and yellowing leaves.

The vine may be damaged. It is possible it was because of cold temperatures in February when they were starting to wake up. This is when plants are the most sensitive to cold. But I doubt it.

If this vine was planted in a landscape, and the soil surface covered in rock to conform to our concept of desert landscaping, then I think you have your answer. The soil has become mineralized. It has no organics left in it.

The reason for leaves turning red and yellow and a lack of healthy growth is due to a loss of plant vigor. Leaves turn color because they are dying and ready to fall off. It just doesn’t have any steam or vigor left so it drops its leaves early, starts thinning out and demonstrates poor growth. If this plant had been surrounded with woodchip mulch instead of rock, then I doubt you would see this problem.

What to do? Rake the rock away from the plant and redistribute it near plants that can tolerate it. Drill or punch holes in the now-bare ground 12 inches from the plant, about 12 inches deep and about 12 inches apart. Apply compost or rich, amended soil in these holes.

These newly applied organics reverse the mineralized soil and help feed the plant, making it vigorous again so it doesn’t become yellow or have poor growth. Cover the soil surrounding the plant with the same compost, about ½ inch deep. Cover this amended soil with woodchips and not rock.

Cut the star jasmine back to about 4 inches in length and let it regrow. New growth will be rapid and dark green.

Cutting it back reinvigorates it. If you don’t cut it back, you will most likely see new, vigorous growth from the base or along its stems close to the base. Cutting it back gets rid of growth that is less vigorous and may be damaged.

Make sure the plant is getting enough water to grow decently and remain healthy. I estimate this plant needs about 5-10 gallons of water each time it’s irrigated. Look at your clock and see how many minutes the valve is operating.

Use at least three drip emitters to supply water to the plant. Size the drip emitters according to how much water the plant needs.

For example, if the number of minutes operating the irrigation valve is 30 minutes, the plant needs at least three each 4-gallons-per-hour emitters (6 gallons). The maximum would be four each 5-gallons-per-hour emitters (10 gallons).

Q: Just read your article today about trimming and fertilizing Texas sage. What kind of fertilizer do you suggest?

A: Texas sage doesn’t require a lot of fertilizer because its desert-adapted. I would use an all-purpose fertilizer such as 16–16 –16. Most places will carry a fertilizer similar and it should be easy to find.

Locate the drip emitters or the source of water. Pull the rock or wood mulch away from the plant with a rake, throw a handful of fertilizer just outside of the emitter and cover it again with the surface mulch.

Fertilizing like this once a year should be enough. Just don’t put the fertilizer within 12 inches of the main trunk or trunks.

Q: I read your fact sheet on local soils and how they can chemically react with concrete in residential homes. I am moving to Las Vegas and would appreciate any information on how to shop for a home that is resistant to water damage issues.

A: That information was published several years ago, and most homes are compliant with the type of cement that should be in contact with our corrosive soils. All cement used in the Mojave Desert is now Type V or Type II modified which resists corrosive soils. Notice the word resists. The secret, though, is to keep soil in contact with surfaces made from cement as dry as possible.

Stucco is made with cement and overhead sprinklers that keep stucco wet cause it to dissolve because of our harsh soils and water. Limit the water from drip emitters and sprinklers from contacting the soil next to the house and from wetting the stucco.

Keep drip irrigation emitters 3 feet from the foundation or flat surfaces made with cement. This sounds like a lot but if you water the plants around the foundation with drip emitters located to the outside of plant and foundation, corrosive soils near the foundation won’t become wet.

For corrosivity to be a problem, water must be present. Keeping soils dry in areas close to concrete reduce corrosion problems.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.