The following is copied and pasted from an eHow I found:

Allelopathy
When plants secrete toxins into the environment to kill nearby competing plants, it's known as allelopathy. The most famous American native tree that is allelopathic is the black walnut tree. However, many juniper shrubs and trees, including eastern red cedar, secret oils and other chemicals that react with the soil to harm other plants. This gives any small red cedar trees an advantage in growing since there are few or no other plants competing for sunlight or water and nutrients in the soil. All junipers tend to dissuade the growth of grasses nearby.
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Not entirely sure if the cedar would be toxic,but it was the first thing that popped into my head.

Here is a link that might be useful: Why Nothing Grows by the cedar tree

This post was edited by asleep_in_the_garden on Wed, Jul 16, 14 at 7:25

I'm not sure it is the cedar, often used for raised beds, although treated wood is better. Containing copper, which is anti-fungal, Fungi are a major problem with vegetables. I spray my fruit trees with copper every year. It is probably too wet, too cold, too hot, or too dry. Hard to tell if you're in Alaska or San Diego, which makes it impossible to give advice. Notice both responses, you can see where we live and what zone we are in (well at least in my case).

How far are plants spaced? A tomato plant needs about 2.5 ft on either side. Mine are now +6 feet or more tall, 3 feet wide.

If it is the cedar is there a liner material that you could recommend for next year.

Any thoughts on the soil mix. How is the soil analysis, I dont know how to interpret the numbers.

I live in Canada in the Toronto area which is close to buffalo about an hour away.

I have six cherry tomatoes plants in each container and keep pinching all suckers to limit plants to two stems.

Wow, they should produce about 4 thousand tomatoes!
Landscape fabric should work as a liner.
Some pictures may help us see the problem.

Here's a few of my tomato plants, just taken a minute ago, peppers in the foreground.

I will post a picture when I get home.

Yes a photo would help and it sounds like you built some nice boxes.

The first red flag for me was the soil used in the container......"blend of compost.....and soil." Normally compost and soil is not recommended for containers because it makes the mix too heavy and water retentive. If you don't mind, what was the name of the product you used? Not sure that's the problem though. When things don't grow well, all things being equal, it's uaually human error of some sort. IMO having no liner is fine, and I wouldn't add one in the future.

Ed, that is where we disagree, I think compost is fantastic for containers, if growing vegetables. After all peat is compost, but I mean manure. You don't use much, just enough to support mycorrhizae, which will build a tremendous root structure. that is the biggest problem I have with the gritty and 5-1-1 mix, sure the soil is structured, yet root growth can be a lot better if compost was used. At least for vegetables. the mix he used clearly is an excellent mix from the breakdown listed. With bonsai, cacti, succulents, and other plants I would not use compost. No one size fits all soil exists.
All my vegetable containers have compost and I'm not having any problems, and many of us use compost.
IMHO it is a myth compost causes poor drainage. too much can, but none is a huge mistake. I still have drying issues using compost, and peat is compost, just replace the peat with a better compost. Peat is one of the worst draining composts around, yet it is in the 5-1-1 mix.
Manure drains a lot better! I still add peat myself because I need MORE water retention with just manure.
even with peat this time of year I water just about daily.

"Compost is rarely used by itself as a potting medium. Compost alone does not have the optimal water holding characteristics" - Vern Grubinger, vegetable and berry specialist
University of Vermont

This post was edited by Drew51 on Wed, Jul 16, 14 at 15:47

Thanks for all the replys so far. I am adding two pictures of the one cedar container I am using. One picture from further back to show the container and one closer up.

The plants colour is looking better but still not very dense.

The last couple weeks I've started watering with more acid water and I've used an epsom salt folier spray twice. The tomatoes are sun gold and sun sugar.

The soil mix is from a company called Gro Bark and the soil is Gro Max which I add more composted pine bark and perlite.

Here is the closer up picture.

Not sure why it upside down sorry. If you click on the picture then its right side up.

Drew51 those are some nice looking plant you have. Its like a dense forest.

tinyfish

It's easy to add zone/location to your name (go to 'your profile') so everybody knows where you are...
Interesting idea about allelophaty...so many people use cedar for raised beds, so far I didn't see "complains" about that.
(GroBark has pretty good products from my experience.)
Your raised beds are nice, look to me deeper than 20"?
Did you plant seeds or transplants?
Was it cold when you planted them?

Maybe you should stop pinching the plants for a while & see what happens.
What is in fertilizer you are using? (Should have 3 numbers)
You said you added some Epsom salts, but it may be too soon to see results.

I see you have some lettuce growing in same bed - how is it doing?
Rina

Got your message. The first thing I see is that the 10-52-10 is delivering far more P than your plants can/will use as a function of the amount of N they use. I would change to a fertilizer with a 2:1:2 or 3:1:2 ratio and supplement with some Pro-TeKt 0-0-3.

Excess P can cause antagonistic deficiencies of several nutrients, but Fe (iron) is most often and usually most affected. It can cause the symptoms you are seeing in your plants.

Your cedar can be allelopathic, but that usually wanes as the presence of volatile terpenoids decreases. If you can't smell the cedar odor, it's not impacting your plants significantly.

Are you sure you're not over-watering? How do you ck soil moisture levels?

Al

Al, your method of using a dowel to check moisture level is a great idea.
The plants look like they have really weak growth. Way too tall with little foliage. It could be too much fertilizer, or not enough light. Tomatoes require full sun all day if possible. At least 8 hours.
When transplanting you can bury the stalk with tomatoes, it will grow roots on the stalk. Often new seedlings are leggy and one should bury them somewhat. You can even dig a trench if really long, put roots at a normal depth, bend stalk down into a trench, then bend it upward at the end of the trench. Cover trench with soil. Just some info for the future.

OK, you say they get enough sun. So stop the MG fertilizer. For one, when young we don't want bloom heavy fertilizers. Too much phosphorus can cause zinc and iron deficiencies which are characterized by yellowing between the leaf veins. Zinc deficiencies
show a bleaching of the tissue. Both iron and zinc
deficiencies occur in the youngest tissues and can occur at the same time, which makes it difficult to identify the actual problem.
Miracle Grow Ultra Bloom is 10-52-10 Holy Moly this is for sure the problem!! That is not good to use on tomatoes! I would flush the beds with water really well and wash that stuff out.
Use Tomato-tone, it will take 2 weeks to work, enough time for your plants to recover.
Tomato-tone is 3-4-6. Follow label directions.
You probably have an iron or zinc deficiency or both.
You can use other fertilizers, but be careful!

Good day all...

When I transplanted the tomatoes, I used a organic granular fertilizer 4-7-7 I believe. I was not using the Miracle Grow at that time. I did not want big leafy plants with no flowers. I started to you the Miracle Grow which is 15-30-15 at a quarter of the label rate when I watered when I started to see the flowers appear. I have M.G. 24-8-16 would that be better. I read using a fertilizer with a higher middle number your plant produce more flowers instead of using a higher first number with gives more growth with less flowers.

I was checking the soil moisture with a moisture meter from the dollar store. A probe with a gage at the top with displays dry to wet. I was only watering once to twice a week.

Three days ago I applied the last of the granular 4-7-7 to the base of the plants at the label rate of 4 tablespoons per plant.

Tony

Tony,

OK, that is a reasonable rate at the right time, and the right strength. Man this is a hard one to figure out.Tomatoes should grow in anything. Not that picky at all.I'm stumped on this one. As far as the growth versus flowers, not really true. Nitrogen does push growth that is true, but phosphorus does not increase flower production. It is needed more when they flower. Phosphorus deficiencies are just about unheard of. It is more of a sales gimmick. Too much nitrogen you get burns around the edges, so even pushing nitrogen has it's limits. It begins to decrease growth with excessive amounts. If you want more flowers don't feed it at all, if the plant thinks it's going to die it will throw out massive amounts of flowers to try and make seed before it goes. What kind of mulch is that? These plants do act like they are inhibited, it could be the cedar. The leggy growth in full sun is puzzling.

The mulch that I used is a pine bark mulch that was not composted. The thickness of the mulch varies from 1"-1.5" around the base of the tomatoes to 0.5" around the few carrots I had planted. The carrorts weren't tall enough to use more mulch.

Drew, Yes I know that compost can be used, but since the OP has a problem I was just looking for potential reasons. I have no problem with using whatever works.

The tomatoes look leggy and underfed, possibly from not enough sun and food. My other thought was that somehow the nitrogen is getting bound up in the mix somehow. At this point I wouldn't worry about 'too' much nitrogen (within reason.) Fertilizer is a good bet, and not the granular type. The others you mentioned are decent.

Not relevant to your issue, but I wanted to say your containers look great!

It does seem that maybe nitrogen is bound up, just a simple soluable would let you know. The plant has to absorb some. But you have been doing this. So my next guess is some form of blight.