Check out Shade Cloth. Maybe you could rig something up like a tent?

Linda

Honestly, unlike us, tomato plants aren't that bothered by high temps. They are tropical plants.

They don't set fruit of course but as long as the plant is kept well watered the plant does fine and kicks back into gear once the heat breaks. 100+ temps are new to you but they are the norm for many of us and we can still grow tomatoes. We just plant much earlier than you may be used to, expect the mid-summer dead zone of production, and just baby the plants until the weather breaks.

Another approach to beat the heat is to plant two crops - one early as possible and then as they die off plant a second Fall crop of plants.

Sure you can rig up shade cloth but it is lots of work and makes for expensive tomatoes.

Dave

I agree with Dave. the plants don't mind the heat. they are smart enough to have have built in defenses for things like heat.. when the it becomes too much for them and they can't get water up fast enough due to water loss, they will start to wilt more and curl up and away from the sun to minimize water loss and sun contact with the leaves, do not water if this happens as it can often be interpreted as lack of water.

There are a lot of questions that can be asked here to help you out.

* How much sun are your plants getting? Are there clear skies every day?

* How much does it rain?

* How insulated is your soil? Our partially clay soil stays quite cool compared to some soils, which get quite hot. I recommend feeling the soil a few to several inches down to see if it's pretty hot or if it's cool (and whether it's still dry that far down). Not all varieties seem to like our soil, though, despite it being cooler in the heat; so, I'm not saying our soil is ideal for every tomato.

* Do you have enough magnesium and potassium? They're supposed to help some with heat-tolerance, but I wouldn't just throw it on willy nilly. You don't want too much of a good thing. Copper may also be a nutrient of note here, as it helps fruits to absorb water, but I don't know how much of a role it plays in heat-tolerance.

* Is it humid, arid or semi-arid in your area?

* What varieties are you growing? This can make a big difference. Some varieties can set fruit well in the heat, but some won't at all until it gets below 90° F. They're considered heat-tolerant if they can set fruit in 90+° F. However, again, you can just wait out the heat.

* What's your soil pH? You might find that a certain pH works best for you in the heat. I tend to think that more acidic soil works better than more alkaline soil for tomatoes in hot temperatures (but maybe it's just my garden).

* How much organic matter is in your soil? I think organic matter probably helps considerably.

* How do you water your plants? Is it just at the base of the plant, or all around so the roots will grow further to get water/nutrients?

* Are your plants in the ground, in containers, in a raised bed, hydroponic or what?

Some plants will have a hard time fruiting in full sun, but can do better with some shade.

As others have said, I wouldn't worry about it too much. They should withstand the temperatures, whether or not they fruit. However, if your soil is magnesium and potassium deficient, is alkaline and/or the soil gets really hot/dry even a foot or two down, and all the plants are in entirely full sun, I might start to worry. You might shade your plants. If it's not too humid, you might shower your plants with a shower nozzle on your hose every couple days—that helps my plants to grow faster, and keeps aphids and whiteflies away. The tomatoes don't seem too bothered by the heat when I do that (but don't splash soil on the leaves, if you can help it). Our waters might be different, though. So, be careful.

I used to grow blueberries, and that's exactly right. They really don't like extreme heat. I don't think shadecloth will make a difference. It's the heat, not the sun. But keep them moist. Water once a day. There are varieties that are more heat tolerant, but be careful. "Heat tolerance" sometimes is strangely used to refer to wintertime, and not summertime temps. As in, such a bush can provide fruit with a small number of chill hours, but may bake just as badly in summer heat.

So far, the tomato plants look OK..one had some brown shriveled leaves in the center but overall looks like it will be fine. 109 is coming and I just didn't know what to expect. I don't want everything to just be gone in a day. Sounds like they'll be OK as long as well watered?

They're in raised beds in a well draining soil mix I bought in bulk and added in compost and manure. I have several varieties.

Shade cloth will help lots. Think sitting in the shade on a hot day. Too warm but ok. Now move in the sun. Sure, you won't die, but you sure wouldn't want to sit there all day. Something like 30-40% opacity should do. Depends how much hours of direct sun your garden gets.

Actually, as noted above, tomatoes will take care of themselves in high heat, as long as they have enough water. We have weeks of 100+ temps down here, and while the tomatoes don't fruit in high heat, they survive and grow fine without added shade. For fruit that you already have on the vine, keeping the soil moist is essential to prevent cracking.

"Think sitting in the shade on a hot day. Too warm but ok. Now move in the sun. Sure, you won't die, but you sure wouldn't want to sit there all day."

It is such comparisons that create the confusion, especially for inexperienced gardeners. I'm hot and suffering so my plants must be hot and suffering too.

Plants are not people. People and plants have totally different thermal systems, very different core temperatures, and very different methods of coping with air temps. And different plants react differently. If blueberry bushes - or lettuce or grass are stressed by heat it does not follow that tomato plants are too.

And as already mentioned, what is unusual weather for someone is often normal weather for many others where the same plants are growing just fine.

Dave

Dave said, "They don't set fruit of course but as long as the plant is kept well
watered the plant does fine and kicks back into gear once the heat
breaks."

Dave - is this true for determinate plants also? I realize the indeterminates will keep on producing flowers all season, but will the determinates? Mine are all flowering right now and we've also been having some horrid humid 95F+ days. I always thought the determinates produce flowers/fruit only once. Of course, I could be misunderstanding the process, as I've never really grown determinates before, and it's been years since I've grown any tomatoes at all.

Jen - regardless of type tomato plants won't set fruit when the night temps consistently remain above 75 and the day temps consistently rises above 95 because the pollen turns tacky and non-viable. When those temps are coupled with high humidity the conditions are even worse. The condition is called "blossom drop" (since the plants drop the blossoms) and there is a FAQ here all about it.

Determinates do not "produce flowers/fruit only once" or all at one time. Flowers are produced throughout their growing cycle until the top terminal bloom sets fruit. Until that happens the plant continues to grow but once that happens the plants are triggered to shift focus and begin to slowly fade.

So yes, assuming intermittent cooler periods of weather a determinate plant can kick in and out of production just like an indeterminate and continue to set fruit off and on until that top terminal trigger happens.

Dave

Love the forum handle, and welcome here if you're new!

You are at a great epicenter, not only for earthquakes, but also for growing tomatoes, smile! Mild night temperatures and California sun to produce all that tomato sweetness. I envy your having that weather - and would not use shade cloth at that location, latitude, on the account of the tomatoes. Just ride out the highs till the weekend, keep the plants hydrated as already covered well by the other comments, and you'll be back in business.

But you asked about your whole garden. Call the local cooperative extension. In Yolo, here (link, phone# on bottom), for example. They will usually bend over backwards to help out with what works best - don't be shy - though some of the helpful 'Master Gardeners' who handle the calls may do it for the love of it, California tax dollars support these programs.

Cheers

PC

Dave, with regard to determinates, can one prolong the fruiting by removing or preventing the top terminal bloom?

can one prolong the fruiting by removing or preventing the top terminal bloom?

Nope. You'd just ... remove the bloom and miss out on the tomatoes. The rest of the plant would be unaffected and life would go on.

Cheers

PC

That's my point. If you remove the terminal blooms, would life go on, and the tomato plant just keep fruiting? The assertion is that terminal blooms are what tell the determinate tomato to stop fruiting.

If I can keep a determinate tomato fruiting, why would I care about the loss of a couple of flowers?

It might prolong it for a very brief period, might get you two terminal buds to form rather than just one...maybe. But not really worth much since most of the lower branches would have already set fruit on their terminal buds so you likely aren't going to get much of anything more out of them.

I know that with some varieties of determinates a small (in size and number) so-called "second crop" is possible in the Fall but the few times I have let one go to that point it has never been worth the trouble. It is much more beneficial IMO to have already replaced the whole plant. To me that is the big advantage of growing determinates in my zone - planted at proper times I can get two full crops in the same amount of time it takes to get 1 crop from an indeterminate.

Dave

When do you start your second crop, Dave? And from seeds or cuttings? Do cuttings work with determinates or just indeterminates?

I believe he has said before that he takes cuttings.

The assertion is that terminal blooms are what tell the determinate tomato to stop fruiting.

That assertion I believe is wrong in this interpretation to prolong fruiting. It would imply the main growing tip dominates fruiting for the entire plant. The main growing tip dominates new vegetative length growth, and flowering for itself.

That would be a fancy way of saying, can I turn my determinate into an indeterminate by cutting the main growing tip.

If you prune the main tip young, another shoot will take its place as the main tip. However the time it takes for this transition of side shoot to main tip will lose you tomatoes. Meanwhile, each determinate tip, including the main and other side shoots will behave with the determinate habit: flower and come to a termination after X times.

The plant will continue growing as normal. Normal for a determinate is hit flower termination in its programmed manner for each tip, whether main or side shoot.

Cheers

PC

I would take the advice of wiser mentors than me, but since I live near you ( Solano County) I will offer this; I think what we do here in California, with long seasons and dry heat in-land, might be different than what people do with heat with humidity. I know not everyone agrees, but with dry heat, shade seems to make a bigger difference in temps Something about solar radiation maybe?. When I am "home" (East and South), shade does not seem to matter as much. I use dappled sun, or under the green shade cloth after about 1 PM when the temps are over 90. I guess I hope it might drop the temp a few degrees, perhaps enough to keep them fruiting a bit longer, and perhaps enough to minimize the splitting that comes with fluctuating soil moisture. Granted my plants are in earth boxes, and in the "summer" I have to fill them at least twice a day. I like to think shade might help with sunscald too.

Maybe it makes little if any difference. I certainly wouldn't lose any sleep over it. I know the plants will survive. BTW, it is almost NEVER hot ( above 70) at night, so I think that doesn't affect fruit set here. One reason I don't plant "early", or try two tomato plantings is that nights/soil is not 50+ until May 1st, and 50+ ends in November. We are Mediterranean, right? Not tropical?

On the other hand, most of my peppers are GREAT in November.

Also, while it seems the triple digits will last forever, and we DO get 30 + days above 90, it does tend to ebb and flow, when the heat gets sucked into the bay, and visa versa. I like to have a supply of flowers on my plants, so that a few will set fruit in the event it cools off for a bit.

Humidity is an interesting factor, and moisture in general. One thing to understand is that the temperature of a leaf is cooler than the air temperature, because of the moisture that evaporates continuously from it. More moisture will evaporate from it when the humidity is low, and so the cooling will be more effective when the humidity is low. BUT, it means that when the humidity is low, plants need to pump water faster, and that water better be available to them.

Moisture on the ground will also cool the ground effectively. That's why deserts are hot. Because the sand is dry. So keeping the soil moist will also cool the local air temperature.

So I'm guessing that for a given air temperature and sunlight, the plants will get hotter when the humidity is high. That's why you feel hotter when the humidity is high. Because you are. Sweat doesn't evaporate as rapidly when the humidity is high.

I think the issue isn't that shade makes things cooler, but that it isn't clear that tomato foiliage, at least, needs to be cooler, if it has enough water to pump.

I think an understated factor in growing tomatoes, which relates to heat and aridity, is wind. We know how food dehydrators work. They have heat and fans to help dry out the food. Wind can be a major contributor to drying out a tomato plant and its soil, too (and in my opinion, it can slow the growth of plants considerably, although it may help them to be tougher in the long run provided the season is long enough and the plant doesn't get completely stunted).

So, this might be one reason people in some areas seem to have real problems with the heat (plants dying, etc., while others don't have major issues). I think alkaline soil, soil temperature, the UV index, and seasonal pests are probably other factors. A really arid area without wind is probably going to be a lot like a somewhat arid area with lots of wind, I'm guessing.

Soil temperature is a factor because the heat affects what nutrients are most available. Extra-hot plants can seem to have magnesium deficiency when there's plenty of magnesium in the soil.

"I think the issue isn't that shade makes things cooler, but that it isn't clear that tomato foiliage, at least, needs to be cooler, if it has enough water to pump."

Tomatoes are said to do best on a certain amount of light. Since more isn't always better (although it often may be), maybe the shade issue is more about light levels than temperature.

One thing to understand is that the temperature of a leaf is cooler than
the air temperature, because of the moisture that evaporates
continuously from it.

Something about solar radiation maybe?.

Nanelle, I'm with you in theory, and the temperature on the leaf and fruit surface can be significantly hotter than the air. Causes sunscald ... from higher temps developed on surfaces.

Evaporation is taking place does not require the leaf temperature to be cooler than ambient. A balance is struck between the amount of water a tomato plant can deliver through transpiration and reflection and the outside temperature. There is a limited capacity - especially in the growing tips and buds. We are outside of that range at over 100 F for sure. In dry climates there is usually a point where the tomato simply can't deliver enough water to all of its transpiring surfaces, and that is when damage and wilt could occur.

The leaf absorbs much of the solar radiation which the air doesn't. The buck stops here when it comes to the solar energy absorbed.

OP mentions wanting a cheaper cover for a 15x15 bed. That to me sounds like they don't want to build a robust support structure, which nanelle, of the kind you might like... and I definitely would too -- one giving plenty of room for air circulation, designed perhaps by angling and placement to reduce midday intensity - which would be great during the hotter days of the season. Just carefully draping (risking damage) it over as a plug for the hot days on demand will certainly help maintain moisture (OP also has mulch they can use to help with that), but could even raise temperatures by restricting air flow and causing a bit of a greenhouse effect (in which case the summer weight fabric would make more sense I think).

So I guess there are a lot of personal situation considerations. To me it is far north enough that the mild nights offset a lot of the problems and will result in reduced production and you probably won't get blocked from set for long periods. I wouldn't want the plants shaded in the morning though, so a bit of engineering would be necessary to get everything satisfactory IMO.

Cheers

PC

> It's
the heat, not the sun.

not sure i quite follow. without the sun there's a huge temperature difference between the sun and shade. ;-)

A moist surface, or a surface that can transpire water, is ALWAYS cooler than a dry surface. That's just evaporation. You feel colder coming out of the swimming pool when you're wet then when you're dry. I'm not convinced that the temperature on a leaf can be hotter than the air temperature. If someone has an IR thermometer, maybe they can check!

The air temperature is *not* set by solar illumination absorbed by the air. If that were the case, the air would be freezing cold. Because that's right, the air absorbs almost no light. The air temperature is set by the ground temperature, and the air hitting the ground and conducting away heat. If the ground is dry, all of that is going to be quite hot.

"If someone has an IR thermometer, maybe they can check!"...I do! Wait....what am I checking?

Here are my plants.

June 2017

July 2016

June 2016

"I'm not convinced that the temperature on a leaf can be hotter than the air temperature"

"The air temperature is *not* set by solar illumination absorbed by the air."

You yourself are explaining exactly how the temperature on a leaf can be hotter than the air temperature. The leaf absorbs light directly from the sun and converts it to heat. The air warms up by being in contact with things generating heat from sunlight, mostly the ground, which is a lot less efficient. Any dark surface in direct sun will be significantly warmer than ambient air, absent other effects (evaporation was mentioned earlier).