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Southwest Yard and Garden

This column comes through the Grant County Extension Service out of New Mexico State University.

blue grama grass rsFigure 1. Blue grama (Bouteloua gracilis), the state grass of New Mexico, photographed in November 2017 near Carson National Forest (photo credit M. Thompson).Question: Do you have recommendations for native grass species for residential landscapes and how to care for them?

- Otero County Extension Master Gardeners

Answer: Bigger ornamental grasses provide beautiful backdrops, hedgerows, and screens in our landscapes. Smaller species help fill in between broadleaf plants and make great garden borders. Both big and small grasses provide texture, contrast, and grace, all with minimal maintenance and zero fertilizer. In winter, when many of our ornamental plants have shed their leaves, grasses can be delightful, even though they're dormant and brown.

blossom end rot rsBlossom end rot on a tomato picked at the NMSU Agricultural Science Center at Los Lunas on August 21 (photo credit M. Thompson).This week, when trying to select a question for the column, I looked through the 22-year archive for this gardening column online (http://aces.nmsu.edu/ces/yard/archives/) to find issues that pop up again and again at this time of year. I selected these three columns written in 1996, 1997, and 2000 by my predecessor, Dr. Curtis Smith, retired NMSU Extension Horticulture Specialist.

pomegranates rsPomegranates split wide open before they were ripe on this backyard tree in Socorro (photo credit V. Gonzales).Question: I have a pomegranate bush, which produced about 30 pomegranates last year. Initially, the pomegranates seemed to be very healthy. However, as the season progressed, prior to ripening, they all began to split open. This year's crop has already started doing the same thing. Is there anything that I can do to prevent all of them from following suit? If not, perhaps you can suggest something that I can do for next season.

- V. Gonzales, Socorro, NM

Answer: My first thought was that splitting is a good sign. My dad knew his pomegranates were ripe when they split. He took great pains to grab the newly split fruit before the ants found them. One year, he even rigged a hammock over the driveway to catch ripe fruit that fell while he was at work because the split ones would explode when they hit the ground.

Splitting before the fruit ripen is a real problem, though. Over the past year, I've gotten this same question from gardeners in Bernalillo, Doña Ana, Otero, and Sierra Counties. Resources from multiple Cooperative Extension programs across the country point to consistent irrigation as the key to keeping pomegranates from splitting too early.
Pomegranates are a low-water-use tree, to be sure, but it's irrigation irregularity that is likely to be the issue. This is because the whole fruit gets bigger and bigger after bloom, but if at some point it is stressed for water, the outer peel may stop growing. Then, when watered, the seeds inside continue to expand and can rupture the leathery peel if it's too tight. This happens with other fruit as well; I'm specifically thinking of tomatoes.

Tree problems are often difficult to diagnose because the symptoms pop up long after the damage was done, so it's hard to know exactly what started it all. Having a regular irrigation schedule for your pomegranate trees can help ensure consistency and reduce early fruit split. Here are recommended guidelines for irrigating established pomegranate trees: Water the entire root zone (at canopy dripline and several feet beyond) to a depth of about 2–3 feet every 7–10 days when temperatures are getting above 90°F. When daytime temperatures are cooler, but still getting above 70°F, back off and irrigate to that same depth every 2–3 weeks. In the winter, irrigating once a month is recommended, but continue to water to the same depth and out beyond the dripline to encourage those powerful, but tiny, lateral roots. If you are like me and you accidentally wait too long between irrigations, don't try to overcompensate with extra water. Pomegranate trees that are water stressed may take up too much water too quickly once it's available, and this can instigate early fruit split.

It's always a good idea to check the soil moisture before watering to be sure you are not overwatering. During monsoon season, you may be tempted to skip an irrigation, but go out and see how deep the rain soaked in before making your decision. Conversely, if we get over a half inch of rain or so, you may very well need to adjust your schedule. Always apply water directly to the ground (preferably mulched ground). Do not spray or sprinkle water on the foliage, flowers, or fruit, because doing so practically invites pathogens, and pomegranate flowers are very sensitive to high humidity.

Splitting fruit was a challenge reported in pomegranate research trials performed by the University of Arizona. The actual cause of splitting was not determined, although it was speculated that uneven watering could have had something to do with it. Researchers noted that 1) after splitting, fruits were more likely to be further damaged by the leaf-footed plant bug and 2) younger trees had more problems with splitting fruit than older trees. They studied 32 cultivars of pomegranates planted at three different elevations: 164, 2,490, and 3,700 feet above sea level.

Conducting pomegranate cultivar trials for residential landscape use across New Mexico is a high priority for me. Pomegranate trees (Punica granatum) are native to the region that stretches from present-day Iran, Afghanistan, Pakistan, and northern India. Through the millennia, they were cultivated to grow in warmer regions of the Mediterranean. Most of the cultivars currently available at nurseries in the U.S. are from that Mediterranean lineage. Therefore, it makes sense that they perform well in California, Arizona, and southern New Mexico. Reference books I checked listed USDA Plant Hardiness Zones 7–10 or 6–8, depending on the pomegranate cultivar. Commercially available cultivars thrive in southern and central New Mexico. Potentially, by testing other cultivars from the original native range, which has much colder winters and lower precipitation than the Mediterranean cultivars, we will find a few that are well adapted for colder parts of our state. Stay tuned!

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the NM Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent (http://aces.nmsu.edu/county/) and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505- 865-7340, ext. 113.

Question:

Other than the novelty, why would a gardener be interested in grafting vegetable plants?

- Yours Truly, Los Lunas, NM

Answer:

I've been hearing more and more about vegetable grafting for commercial production and wanted to know more, so I posed this week's question myself.

Grafting, in general, is a common method for propagating plants by carefully joining cut plant parts so they grow together as one plant. Many plants can be propagated from seed or from cuttings that put out new roots. Others — like apples — don't "grow true" from seed or root easily from cuttings and must be grafted. Every apple you've ever eaten is from a grafted apple tree (unless you've eaten crabapples) where a small branch cut from a desirable apple tree was then grafted onto the trunk of an apple variety with desirable roots. "Desirable" means different things depending on if you're talking about the top portion (scion) of the grafted plant or the bottom (rootstock). Desirable scion traits might include flowering time, fruit flavor, or branching pattern. Desirable rootstock traits could involve rooting vigor, disease resistance, or salt tolerance, depending on local factors.

In much of the woody plant realm (i.e., most fruit trees and many landscape perennials), grafting is standard, even though grafting is expensive because it takes skill and time. Even with perfect growing conditions and skillful technique, the graft may not "take," for example, if the cut edges of the two plants are not lined up properly, or a pathogen infects the tissue. The costs of grafting are reflected partly in the high sales prices on fruit trees and other grafted specimens. But these plants are expected to live year after year (hence, "perennial") and there may be an added benefit if growing from seed or cuttings is not an option.

So, grafting makes sense for some perennial species. Now let's consider vegetable plants, like tomatoes or watermelons, which are grown as annuals, meaning they complete their entire life cycle in one growing season. Grafting is also expensive in the vegetable crop world. Understandably, grafting vegetables is not very common in New Mexico vegetable production. You won't likely find vegetables at local farmers markets here that were harvested from grafted plants. That's partly because direct-seeding row vegetable crops can be more economical than transplanting. Grafting after plants are in the field is not a viable option because they need serious babying (high humidity and low environmental stressors) for the grafts to take successfully. At a horticulture conference last week, Dr. Brian Ward, Organic Vegetable Specialist at Clemson University, gave me a quick grafting demo. With his permission, I videotaped the tutorial. To watch it, visit https://nmsudesertblooms.blogspot.com/.

Dr. Ward provided a great example of how vegetable grafting becomes advantageous when a soil-borne disease is known to devastate the roots of a desired variety of, in this case, watermelon, but another watermelon variety makes good rootstock because it develops roots that are resistant to that same disease.

If better rootstocks aren't an option, disease issues in New Mexico will not be remedied by grafting. Other ways that grafting might benefit our vegetable growers include improving plant salt tolerance, cold tolerance, water use efficiency, or nutrient use efficiency. Can you see now why this trend is growing and how important experimental research is in this field? At http://www.vegetablegrafting.org/, a research-based information portal, you can tap into research and education programs being conducted all over the world. As a home gardener, you too can experience the pros and cons of grafting vegetable plants. It's tricky to be sure, but you just might be able to bask in the "grafterglow" of success.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the NM Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent (http://aces.nmsu.edu/county/)  and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505- 865-7340, ext. 113.

fig rsBig figs on a tree somewhere* on the NMSU main campus in Las Cruces in September 2015
(photo credit M. Thompson).
*Email me at desertblooms@nmsu.edu for hints on where to find this particular tree.

Question:

What is the best time of year to grow fig trees from cuttings?

- Rod B., Rio Rancho, NM

Answer:

The short answer: not now. Fig trees (Ficus carica) are one of the relatively few species that propagate easier from hardwood cuttings than softwood. Hardwood just means dormant, older growth. Softwood, by comparison, is the soft, usually green, new season growth. So, the best time to harvest the wood for fig propagation is in the wintertime (January–February).

A greater number of woody species are propagated using softwood cuttings, including ginkgo, lilac, redbud, sumac, and wisteria. Others still can be propagated by either method, but there are different tricks for each.

I asked Dr. Margaret Pooler, a researcher and woody plant breeder with the USDA U.S. National Arboretum (http://usna.usda.gov), to explain differences between propagation methods for woody plant cuttings. She said that they usually use softwood or semi-hardwood cuttings because roots develop more readily than with hardwood cuttings, and semi-hardwood cuttings aren't quite as floppy and difficult to manage compared to softwood cuttings. The drawback of softwood is that it is very susceptible to drying out, so providing high humidity is key.

For hardwood cuttings, the opposite is true—don't let the bare sticks get too wet and rot before roots have a chance to establish.

Rooting hormone is recommended for the home gardener when attempting propagation from cuttings. You can get it from your local garden center in a powder or liquid form and apply it to the open wound before placing the cut end in the soil. Be sure to follow label directions. Visit https://nmsudesertblooms.blogspot.com for tips on proper cutting angle, location, and care.

I also asked Dr. Pooler why rooting hormone helps root development when propagating from cuttings, but has not been shown to increase rooting when they are transplanted in the landscape. She pointed out that roots naturally make their own rooting hormones, so when root tissues have already developed, there's no need for added root stimulant.

Collecting and planting seeds is the easiest way to propagate lots of woody and herbaceous (non-woody) species. For more information, see the NMSU Extension Guide H-112, "Seed Propagation of Plants" (http://aces.nmsu.edu/pubs/_h/H112/welcome.html).

I've said it before and I'll say it again: I'm a big fig fan. To be clear, I like both large and small figs, bigly. My Las Cruces sources informed me that local figs started ripening a few weeks ago, and many fig trees are at their prime this week in Albuquerque (Fig. 2).
 
fig drying rack rsFig drying rack in Albuquerque. Luckily, these were not hurt by recent hailstorms
(photo credit M. Cohen).

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the NM Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent (http://aces.nmsu.edu/county/) and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505- 865-7340, ext. 113.

Question:

What’s growing on the underside of my neighbor’s sunflower leaves?

Carl M., Los Lunas, NM

Question:

We are building our Extension Master Gardener library. What are your favorite plant books?
- Lin Y., Valencia County, NM

Answer:

Southwest Yard & Garden by Dr. Marisa Thompson

saltcedarFigure 1. Invasive saltcedar, also known as tamarisk, near Isleta Pueblo (photo credit M. Thompson

I have a saltcedar I inherited when I moved into my rental home in Zuni, NM. I have cut it back to a stump as best I could without a chainsaw or any power tools, but it incessantly puts out shoots and tries to stage a comeback. What is the simplest way to permanently kill this invasive beast?
- Tammy P., Zuni, NM

Answer:
You are not alone in your saltcedar frustrations. I invited NMSU Extension Weed Specialist, Dr. Leslie Beck, to review your options: