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big zac tomato
Big Zac Tomato

Growing Tomatoes in Las Cruces
Lycopersicon esculentum
Family – Solanaceae

All too often, this most sought after garden fruit proves elusive to Las Cruces gardeners.
Based on what I have seen and heard, the reasons are both universal to every climate and specific to southern New Mexico. Those reasons are:

• Cold – both the killing kind and cold that slows growth, making the plants more vulnerable to stressors

• Heat – that effects plant growth as well as blossom retention and fruit setting

• Wind – particularly in spring when plants are young and tender

• Diseases – from spring through harvest

• Fruit Stress – some exacerbated by local soil conditions as well as cold, heat and water stress

Cold and Heat Stress

In our region, cold, heat and wind factors are really timing issues – so let’s start with cold. If you have to start growing tomatoes early in the season, select cold tolerant, early varieties. My favorite (grown every year) is Oregon Spring Bush. Grow them indoors or in a green house under lights and pot them up until they are ready to start blooming. When transplanting them out before the last frost, protect them with frost blankets, wall-o-waters or some kind of cover.

The chart below shows the spring and second season timing for tomatoes. Even then, it’s not the whole picture of possibilities. Extension publications recommend a spring planting date of Feb 15 – Mar 15 only. If you start seed indoors on Jan 15 and pot them up midway, you can still plant out on March 15. You can also start later and reduce the risk of cold and heat stress even further.

tomato chart

You can avoid cold and most heat stressors by altering your timing so that you are growing in the optimum temperature range for tomatoes, but you will not get the award for the first tomato of the season.

tomatoe Temperatures

Optimum nighttime temperatures for tomatoes (above 55°F) begin here in early to mid May. If you plan to transplant out then, your plants will have the best of growing conditions and not spend many nights and days stalled out waiting for warm temperatures. Since June is our hottest month, it is the time when most blossom drop occurs. Transplants set out in May will begin to bloom after the peak heat and produce tomatoes during late July and August, depending on varieties and growing conditions.

The heat stress that is most noticeable occurs with days temperatures above 90°F. However, nighttime temperatures above 76°F also cause heat stress that leads to blossom drop. Increasing the humidity around the plants will reduce overall stress during peak heat times and reduce blossom drop. Using fabric row covers (Agribond) will increase humidity enough to reduce blossom drop, but not eliminate it. Once the monsoon rains begin, remove the row covers to avoid fungal diseases fostered by excess humidity.

Second Season Tomatoes

Our growing season here is so long, that you can even start a second crop in June and get a good harvest before frost, without any cold or heat stress; however, an early frost remains a risk




Wind Stress

You have two choices – protection or late planting. The best wind protectors are row covers. Next best are windbreaks. Setting plants out in May avoids the worst of the windy season.

tomato covers
Tomato row cover and protective skirt

Disease

Curly-top Virus
Row covers and windbreak/skirts will protect tomatoes from leafhopper transmitted curly top virus. Growing tomatoes dependably requires using some protection from leafhoppers – period. Thirty-inch tall skirts will stop nearly all leafhoppers and can be left on through the season as the plants grow out the tops.

Other Common Tomato Diseases
Cornell Vegetable MD Online is one of the best sites for information on tomato diseases
(http://vegetablemdonline.ppath.cornell.edu/diagnostickeys/TomWlt/TomWiltKey.html)

Fruit Stress

The goal of growing tomatoes is to produce quality fruit; however, there are many pitfalls on the road to ripe and juicy.
Blossom End-Rot – is common here because of our high soil pH that can further limit calcium availability during periods of water stress.
Cracking - is common here during the monsoon season when soil water levels fluctuate
Catfacing - is common if you plant early enough for flowering to occur during cold weather or if you over fertilize young plant.
Sunburn - is very common here if shaded fruit is exposed to direct sun light.

The article Blemishes on the Road to Ripe and Juicy describes the common fruit problems and provides solutions.

So there you have it, in a nutshell - what to do here to increase your success with tomato production. Using good culturing practices, creating optimum soil conditions, watering properly and choosing the right varieties are also required to be dependably successful.

Good Gardening and Good Eating,

Darrol Shillingburg
Doña Ana Extension Master Gardener
March 2011

 

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