Information on raised bed gardening specific to Las Vegas

Requests for Dr. Sylvan Wittwer’s information on raised bed gardening, his bible I call it, overwhelmed and surprised me. I just finished sending out copies to everyone and my fingers are tired.

Dr. Wittwer was the former vegetable extension specialist for Michigan State University before he retired to Southern Nevada. In Logandale, he maintained a large in-ground vegetable garden for many years before moving and eventually passing away. Logandale, in its agricultural area called the Moapa Valley and located about 60 miles north of Las Vegas, is slightly warmer but has similar soils and climate.

It is essential to use his recommended varieties but his recommendations on fertilizers and pesticides can be substituted for more organic forms if you prefer. When using raised beds, or Mel Bartholomew’s “square-foot gardening,” look for more compact forms of the same variety.

Vegetable breeders earn their pay by recognizing popular varieties in regions that would be even more popular with homeowners provided they have enough space to grow them. They concentrate on making them small or changing their fruiting habits somehow. The Early Girl variety of tomato is now available as a bush or determinate type instead of the continuously vining type called indeterminate.

There are many reasons for constructing raised beds: rocky soil beneath it, uninhabitable because of pests like nematodes, small space requirements, beautification, etc. A type of raised bed is a nursery container. Even smaller raised beds such as ornamental containers in the landscape can add beauty and height to traditional gardens.

Unlike larger raised beds, containers be easily emptied, scrubbed clean and refilled again with new soil. Remember to fill them to within 1 inch of the container lip to maximize their soil depth and ease their heat dissipation.

Remember pots get hot on the outside unless the pot has something shading it. Double potting them (so they have an air space) is one answer to keep the heat under control.

Q: We wanted to build a raised garden bed in a rocky spot. I wanted to build a raised bed 18 inches high and fill it with quality soil. On second thought, it seems to me that digging deep into our native soil and then backfilling that sunken area with quality soil helps retain moisture, reduces the soil from being baked by the sun and keeps plant roots cooler. Is this something you would recommend?

A: You don’t need anything 18 inches deep. Twelve inches are plenty deep enough for all vegetables and herbs. Plus having a rock-free growing soil benefits root crops like carrots and asparagus spears so they grow straight and don’t get forked or crooked.

Yes, it’s true growing in the ground, as opposed to a raised bed, uses less water, but applying water to a raised bed close to the exposed wood helps keep the roots moist on hot days.

Either method works but your raised bed option requires less work overall. Traditional side walls of untreated redwood or cedar last about 10 years. Even pine side walls, treated or untreated, last nearly as long. Just don’t bury them.

The only thing I would add is that a 2-foot-wide bed is a bit wide unless you are 5-foot-10 or taller. A better width to consider for shorter people is 40 to 42 inches.

Another option to consider is plastic nursery containers. The nice thing about containers is that they can be moved to a new spot.

Containers are very flexible in growing operations. They can be used for starting seedlings and pushed together, and grown further apart when needed. However, I wish there were more square containers available.

Mulching new seeds during the heat is important for temperature and moisture control. If you don’t, one dry hot day is enough for you to quit. I use a light application of horse bedding (one-quarter inch deep layer over the seeds, just enough to keep the sun off the soil) to help keep the seeds cooler and moist.

Q: Which fruit trees are best planted in rocky soil?

A: Rocky soil, to me, means soils low in organic content as well as full of rocks. In the desert, these soils may be growing fruit trees that are productive but can handle soils covered in rock on the surface of the soil better than some other fruit trees. I am guessing this definition could be extended into prepared soil covered with a two to 3-inch layer of rock.

Stone fruit trees are like apricots, plums and peaches; those trees that produce fruit have a hard pit in the center. Stone fruit trees are among the best trees, in general, to grow in rocky soil because of their root’s tolerances to low soil organics, root structure and ability to suck up water from the soil at low levels of soil moisture.

Fig trees can get large, over 40 feet tall, but they also can handle severe pruning to keep them smaller. We have done that over and over at the university orchard in North Las Vegas and have had no issues with it for 15 years.

Remember to give them extra water, above and beyond what they need for their growth, if you want them to hang on to their fruit and be productive. Unlike their water needs for growth, they need more water to produce fruit during the hot summers.

Olive trees make it onto my list of recommended fruit trees to grow in rocky and low organic soils even though it is not used that much by some. Olives can be grown (outside Clark County) for fruit production. The fruit is either used as a condiment (green or black fruit) or the fruit is extracted for its oil (olive oil) or both.

Citrus is probably the most often asked-about fruit tree regarding soil organics. Yes, there are huge differences between citrus and their organic requirements.

Most citrus trees are tropical to semitropical which include true lemons, oranges, clementines and grapefruit. All four of these types of citrus do OK in rocky soils or grown under rocky surface mulch.

Q: I have read that Leucophyllum frutescens (Texas sage or Texas ranger) should not be fertilized, but I have also read that a light spring application of a nitrogen fertilizer is helpful. What do you say? And if fertilizer is appropriate, what should the ratio be and when should it be applied?

A: Most natives such as Texas ranger don’t need a lot of fertilizer, but they will get larger and healthier from small applications made frequently. If you haven’t applied any, then a 16-16-16 or equivalent fertilizer high in all three NPKs (nitrogen, phosphorus, and potassium) is probably beneficial.

If you apply fertilizer to any winter-tender plants (not saying Texas ranger is cold sensitive in Las Vegas), then avoid applications of a high nitrogen fertilizer (fertilizers high in phosphorus or potassium either alone or combined are fine, but not nitrogen) after July or Aug. 1. That goes for plants sensitive to winter cold temperatures below 25 degrees.

Q: We have a mixture of ornamental and edible trees in our yard. I want to stay away from synthetic products. What fertilizer can I use that is affordable but is also natural/organic that would give an ample amount of nutrients? Does fish emulsion and seaweed extract offer enough NPK for large trees? How often during growing months?

A: Yes, but you need a lot of it. Fish emulsion typically contains an actual NPK content of a 4-1-1, while seaweed extract contains around 1-0-4. If they are combined into one fertilizer as a liquid it will contain about 2.5-0.5-2.5. One example of a synthetic fertilizer is 16-16-16.

If we just look at the nitrogen content, we would need over six times as much nitrogen to have a similar nitrogen content. The good news is if it is applied slowly over six to eight months, we could get by with maybe only three or four times as much instead of six.

My advice to you is to consider a fertilizer injector for your property and possibly a second one for your vegetable bed. As long as a fertilizer is USDA organic approved and suitable for fertilizer injectors (totally water soluble). it will work to satisfy your needs.

I would suggest mixing it with water to the manufacturers’ recommendations and place the injector at the lowest setting for injecting this fertilizer. Organic fertilizers are available online either from Drip Works or Grow Organic as well as the injectors.

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.