How to grow tomatoes in Southern Arizona

7 tips for your best tomatoes ever

1 - Use Epsom salt (magnesium sulfate) in each planting hole. Mix 1-2 tablespoons into the soil when transplanting. Epsom salt will increase the amount of calcium available to the plants and help prevent blossom end rot. If you do see yellowish-leaves or blossom-end rot (a blackish spot at the bottom of the fruit), mix 1-2 tablespoons per gallon of water and spray the foliage.

Another strategy is to use the foliar spray when transplanting, when the plant first starts flowering and when the fruit is setting.

Peppers are susceptible to the same problem, so give them a boost with Epsom salt, too.

2 - Use the just right amount of organic nitrogen. This one's a little tricky: use too much and you'll get big, leafy plants and few blossoms or fruit. Too little and the foliage won't develop properly and the plant will fail to thrive. I've made both mistakes, so all I can say is, experiment.

When transplanting, use well-aged manure and compost mixed in with your garden soil. If you find that your plants are not leafing out properly, give them a boost of manure tea or fish emulsion mixed in water.

Part 1: 10 things to know about growing tomatoes

Ah, tomatoes — that heavenly slice of summer. There’s no other vegetable — well, technically it's a fruit — that tastes so wonderful when home grown versus store bought. But if you’ve tried to grow them here in Tucson, you know they can be finicky. Chances are you’ve had a little success — and a lot of failures.

Last summer my tomatoes did really well in the spring — they grew fast, bushed out nicely and produced lots of leaves. But there weren’t many flowers and they didn’t develop into actual fruit. Sound familiar?

If you have a chance to take a class at Harlow Gardens or another nursery, do take advantage of it. People at a recent class all seemed to have a lot of "ah-hah" moments. The follow-up questions were good, and our instructor covered in-ground and container gardening, too.

So read on for some expert advice from the class; after 20 minutes of listening to garden guru Carolyn Smith I had figured out my biggest mistake. You’ll probably recognize your own mistakes in the following list.

Timing:

It’s OK to plant now, but some gardeners did so in February, especially given our early spring. March 15 is our average frost-free date but it’s not a hard and fast guideline, so now's the time to get those transplants in.

What's new:

New and gaining in popularity are grafted tomato plants. Why? They have a sturdier rootstock that can take our brutal summer heat. They grow faster, produce more fruit and are said to be more resistant to diseases and pests.

Look for both cherry and regular grafted tomatoes in nurseries. How do you know they’re grafted? They should be marked as such, plus if you look closely at the stem you’ll see a little clip. You should leave the clip alone; it will pop off by itself as it grows, Carolyn says.

As you’d expect, they cost more — twice as much, in fact. But considering what you’d pay per tomato at the farmers market, it’s probably worth it.

Where to plant:

For your summer garden, try to get some afternoon shade. You want plants to get plenty of morning sun — at least four to six hours a day. A deciduous tree that casts shade later in the day would work, or use a shade cloth.

Container tip: Your pots should be 20 inches in diameter minimum and at least 15 inches deep, unless you’re growing a compact variety. If you’re using containers, choose the smaller varieties. Also it should be noted: plant just one plant per pot and don’t plant anything else with it or it’ll compete for water and nutrients.

James Wood / Arizona Daily Star 2009

Tilling, fertilizing and planting

Till 2-3 feet down for your summer garden. (Winter gardens don’t have to be as deep.) Add 3-4 inches of organic compost and till that in. Here’s my big mistake: Don’t use manure for summer crops like tomatoes, even if it’s well aged. What’s the problem with manure? It’s too “hot” for the roots and can lead to blossom-end rot. (More on that later.) Use compost instead or try worm castings. They keep the soil loose and add beneficial nutrients. (A couple of live worms would be a bonus.) Again, organic compost is best because it releases nutrients slowly over the season.
Don’t use synthetic fertilizers. It was music to my organic ears to hear Carolyn say that. Why? Organic matter helps build the soil, doesn’t harm good microorganisms and releases nutrients slowly. It rarely burns the plants — and only if you overapply it. So follow directions. When it comes to fertilizer, “More is not better.” Well said, Carolyn. Also, fertilize your heavy feeders regularly throughout the summer. I usually make a compost tea and water it in once a month or so.
Pinch off the very bottom leaves and put the plant deeper in the ground than it was in the pot — up to the second set of leaves. Stake each plant to keep it from flopping over.

Tomatoes, Part 3: Watering, selecting the right variety

Besides soil, the biggest key to successful gardening in the desert is ...

Watering:

Here’s another thing I was doing wrong. Always water in the morning. Common sense, right? Your plants should be completely hydrated before they face the heat of the day. If you water in the evening, the smaller roots are likely to rot. Be sure to water every day once daily temps hit 85 degrees. In extreme heat, try watering in the morning and late afternoon.

Try to keep your tomato plants evenly moist: Water to about 2 feet down. Let the soil dry to a depth of 4-6 inches then water deeply again. Leech soils by watering more heavily about once a month.
Container tip: Water every day but don’t allow it to collect in the saucer. Dump it out or, if the pot’s heavy, use an old turkey baster to siphon it out.

Poor fruit set:

Alas, it could be a lack of pollinators. I have definitely noticed an absence of bees in general. Most gardeners have heard of Colony Collapse Disorder, but Google it if you haven’t. In the meantime, don’t use chemical sprays and pesticides — they’ll harm bees. Do plant flowers that attract bees; it’s especially beneficial for squash and cucumbers. I tend to let some things, such as basil or broccoli, flower and go to seed because the bees love them. And if you’re lucky, they’ll stick around long enough to pollinate everything else.

Solution 1: Blossom set spray. This is a natural plant hormone that keeps the blossom around a little longer so it has a better chance of getting pollinated. Spray it on the flowers of peppers, squash and cucumbers, too.
Solution 2: Use an artist’s paintbrush or a Q-tip in the early morning to touch all of the blossoms.

Other causes are extreme temperatures, dry soils, too much shade or too much nitrogen.

What varieties to plant?

This is the fun part: Beefsteaks or Romas? Cherry or grape? Yellow or red? Chocolate or heirloom? Honestly, Harlow carries so many varieties that my hand cramped just trying to write a list of them. They carry about 35 varieties, Carolyn says. Plant two or three different varieties to hedge your bets. Why not try at least one heirloom? They tend to be more flavorful and were carefully saved and passed down by our grandparents and great-grandparents.

Here are some that I would grow just for the cool names:

Green Zebra
Mr. Stripey
Cherokee Chocolate
Indigo Rose (a purple tomato)
Heat Wave (a heat-loving variety, naturally)

Size:

Go for midsize or smaller. They’re less likely to split and will ripen earlier. Grape and cherry tomatoes withstand the heat better and should produce throughout the summer.

Random tip:

Plant yellow tomatoes if you're prone to heartburn — they are less acidic and easier on the stomach.

How to grow tomatoes in Southern Arizona