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Monday, May 6, 2013

Tomatoes Not Setting Fruit? Shake It Up Baby!

Q. I have only gotten into gardening in the Vegas area the last 3 years and have been successfully growing tomatoes the first 2 years. But I noticed last year that I didn't get nearly the same number of tomatoes that I harvested in previous years. I have a raised bed that I started with a blend of about 4:1 of cheap compost and our desert soil.  The soil level is at least 2 1/2 feet deep.  Each year I have continued adding compost from my own yard and vegetable scraps, at least 3-4 inches of compost each year. I have periodically used a Star Nursery fertilizer as well (the one designated "for vegetables/fruits"). 
The watering for the tomatoes is set to a timer such that during the full heat of summer the plants get watered twice a day (about 10 minutes each time), less frequently when the temperatures are lower. There is microtubing with an adjustable drip emitter used to water the plants. The watering scheme has been unchanged the past 3 years. The plants get full sun all day.

So last year the tomato plants themselves grew well and I saw lots of flowers, but the tomatoes just never developed. This was even before the heat of summer hit. I think I harvested about a third of what I did the year before.
I noticed a lot less honey bees this past year in general as well. I have grown other mixed vegetables that have all done well so I am assuming the nutrient content in the soil is ok. Is there anything I could be doing differently to help get more tomatoes?  What about Mason bees? Are there flowers I can plant to attract bees for better pollination?

A.  Let's look at the list of things that could affect fruit production. These would include the right temperature range, wind, good soil preparation, disease, pollinators such as bees, humidity, sunlight and a few other things as well. If we have a long, cool spring we can expect to potentially have good production of fruit. If the spring is erratic and goes from cold to hot in a short period of time we can expect poor fruit production. I will tell you a little trick you can use in a bit but I want to make sure you read the rest of what I have to say. Little tricks do not work all by themselves. You have to do the whole package to be truly successful.


Irregular Production

Let me first comment on the irregular tomato production. Our desert climate is not the best climate for tomato production. We have a very short spring sometimes. The spring months as well as the corresponding fall weather, are the best times for tomato production here. When it gets too hot, tomatoes stop producing. Tomatoes are very sensitive to both hot and cold weather and have a more narrow acceptable temperature range than peppers or eggplant which are in the same family.
Tomatoes do not set well above 90°F and don't set it all when it stops 95°F. If bees are not working during the cooler parts of the day, you will get poor fruit set. Pollinators are very important and if they are not working when you need them or they have a very narrow window of opportunity then production will be down. Fruit set in the cool spring usually means you will get tomatoes in June and July and then they stop producing Et al. in August because it was too hot for fruit set.

Soil Improvement

Desert soils that are raw (never in production before) are ripped deep with an irrigation
trencher prior to preparation to open the soil for organic matter additions.
You have to be very careful about compost and if you use cheap compost your garden could be in trouble. When I prepare our desert soil for production I use an equal mix of good compost and native soil to begin with and I construct raised beds with outside walls. I will use compost that I know is good quality or make my own. I emphasize this... there is no good quality compost available for sale in Las Vegas. They are making some compost at the Las Vegas Springs preserve which is pretty good stuff but they are not allowed to sell it. 
The second year of production I add about half of the amount I used the first year. The third-year I add about the same amount as the second year. By the third year, that desert soil will become extremely productive. At that point, I only add compost to the area that I'm planting, not the entire growing area.

 I typically modify the soil to a depth of about 12 to 18 inches. However, I do rip the soil as deep as I can with an irrigation trencher when I first began constructing the raised beds.

 I strongly suggest not to use any compost without knowing what's in it. I am going to put a caveat here... the last time I looked one bagged compost that didn't seem too bad was Kellogg's. However, I believe they were using biosolids from Southern California. I believe the bag said not to use it for vegetables. I think this was available either from Lowe's or Home Depot but I have not looked for quite a while.

Good Varieties

Yellow pear tomato
You don't mention which varieties of tomatoes you are using and that can have a huge impact on production. Usually, varieties like Early Girl, Celebrity, Jet Star, Big Boy, Better Boy, and a grape tomatoes, yellow pear and cherry tomatoes will set when others do not. A couple of those plants are good indicators that least you are getting pollination.

Check your varieties and make sure they get in early. Try to keep them out of windy locations and you mention full sunlight but make sure they have a minimum of six hours.

Pollination and Pollinators

 It is not just getting flowers that are heat tolerant, you need flowers that are blooming at the right time as your tomatoes. Having bees coming to your yard during the heat will not help tomato production. They need to be blooming at the same time and this usually means spring flowering perennials and fruit trees.

I was only taking a guess about mason bees. Rather than encourage that type of be which might struggle in our climate I would encourage you to look at our native leafcutter bees which pollinate alfalfa and other legumes. You might also consider clovers and other legumes as a mix for attracting bees.

Finally the Hint

There are two ways of getting tomatoes to set fruit without pollinators. One is the use of applied hormones you can spray on the flowers to set fruit (parthenocarpically) without bees. These are sprays you can buy in the nursery.

The second method is a technique that green house growers use when they grow tomatoes because they dont have pollinators in their houses either. An electric toothbrush. It appears that the physical visit of a bee to the flower is not the only thing that trips the setting of fruit but the vibration caused by the wings of the bees. So when temperatures are good and you see flowers, walk over to your tomatoes and gently flick the flower clusters with your finger or use an electric toothbrush and vibrate the flower clusters for a few seconds to improve flower set.


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