Why are my tomato leaves turning yellow?
Tomato plants leaves turn yellow for many different reasons. Here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/vegetables/tomato/yellow-tomato-leaves.htm
I recently purchased a 25 pellet Jiffy greenhouse. It's 25 small peat pellets and right now 16 have sprouted up seedlings. The tomato seedlings seem to be growing the quickest--how do I know when to place them in a bigger pot? I don't want to keep the top of the greenhouse on if it's going to be detrimental for the plants already growing. Help!
As soon as the seeds germinate, you should take off the cover, so the seedlings can get plenty of light. You can plant the seedling pots as soon as the seedling has 3-4 true leaves. Here are some articles to help: https://www.gardeningknowhow.com/edible/vegetables/tomato/growing-tomatoes-from-seed.htm
https://www.gardeningknowhow.com/edible/vegetables/tomato/planting-tomato-plants.htm
New tomato leaves turning yellow on transplants as well as established plants. I've attached photo for assessment. Diagnosis and help would be greatly appreciated.
There are lot of reasons your tomatoes may be turning yellow and diagnosis can be tricky.
It's possible your soil lacks nutrients, so you may want to have your soil tested by a lab. You can also purchase DIY soil tests at garden centers.
There's also a good possibility your plants are diseased. If so, this should help you diagnose the problem:https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-diseases.htm
I sprayed a systemic herbicide to kill herbs about four days before transplanting my tomato. Will this have an effect on the tomato plants?
This article will help you - typically a waiting period of 3 days is recommended which you have done, so your tomatoes should be ok.
Cut open a tomato and it had sprouts in it. Can these be used for tomato plants?
Yes, they can! Here is a webpage where somebody did that with great success:
http://www.treehugger.com/lawn-garden/tomato-seeds-amazingly-sprouting-inside-tomato-photos.html
When removing suckers on Hybrid determinate type, and rooting those, will the rooted suckers increase the growing season?
Yes, growing tomato plants from suckers is a good way to extend your harvest into the autumn months.
Tomatoes - leaves turn yellow, then brown and finally die. Starts with the lowest leaves and works it way upward. Does not seem to affect the fruit.
There are many possibilities ranging from insect pests, environmental conditions or disease.
It could be 'bacterial canker'. When tomatoes have bacterial canker, their leaves will wilt, turn yellow then brown and die from the bottom up.
It could be a wilt disease, such as fusarium or verticillium, for which there is no chemical treatment. Solarization of the soil is typically recommended. The YouTube video below will help you identify if you have a wilt disease or not.
https://www.youtube.com/watch?v=EOTi7srQJsY
Over/under-watering will also cause leaves to turn yellow and wilt. Examine the soil. If it is dry, dusty and cracked, then your plants are under-watered. If the soil seems swampy, the plants are most likely over-watered.
For more information on all of the above, I recommend you review the following article:
https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-plant-problems.htm