Yellowing leaves at bottom of tomato plant

I have a couple 4ft tall tomato plants in a 3 ft raised bed with good draining soil, mulched that have been thriving. Just recently they've begun to get yellow leaves toward the bottom of the plant. They then are getting crispy and appear to be dying off. I'd read elsewhere this might be common when fruiting and those leaves that may be more shaded. Does that sound like fair advice? Might I need to change something?

Thanks in advance.

It's normal....mostly folks just snap those off as they are close to the ground and can promote fungal growth when always damp from ground contact. When they have lost their chlorophyll they have lost the ability to process nutrition anyway, so they are of no use.

Sound right to me, thats what those things do. Pull the leaves if you have the need to take action. When they first start to yellow, pluck them, put in a blender, puree, strain off the juice...makes a fine foliar spray to drive off bugs from your other plants

There is a chance that what is going on is Chlorosis. You'll see this in an extremely dry or wet period. When a plant is not getting enough nutrients, the older (usually bottom) leaves will be sacrificed to keep the rest of the plant going. If you have other plants with yellowing bottom leaves, grab the hose and give everything a deep soaking or dig a drainage ditch. Pay no heed to the cotyledons, the first leaves from germination, their yellowing is also normal.

to prevent diseases do not splash soil up onto the leaves when watering..mulch is helpful but doesn't always prevent diseases..best to use a drip system when irrigating rather than a sprinkler or hose system.

I used to think yellowing was a natural occurance with tomatoes then I learned that ir could be a blight so would carefully cull any plants as they developed any yellowing. Now, for the last several years, I apply 1 tsp epsom salt (an accepted ammendment in organic gardening) per foot of plant as a magneseum supplement. It works for me...the whole plant stays green with no lower leaf yellowing and produces from June into the fall unless it gets too hot to set fruit. I haven't figured out why our soil/compost would lack magneseum though.
If yellowing of leaves runs up the plant I would still suspect disease and cull the plant esp. if they are close together and the blight could travel from plant to plant easily.
I also mulch and clip lower leaves so nothing is touching the ground.

Yellowing of the lower leaves may be a sign of slight strain, especially during fruiting. The plant focuses it's energy and nutrients on its offspring, which means any nutrients that are mobile in the lower leaves (such as nitrogen) leave. This makes the lower leaves look less healthy. If it otherwise seems to be doing fine, you may just accept that and let the plant be. You could add more fertilizer, but at this late in the game, it may be too late. Just consider it for next year. On the other hand, if water is splashng on the leaves and their pretty shaded, it could be disease...or both.

These are good ideas. I think I'll prune off those yellowing leaves. Some have turned crunchy. My fear was that afterward the yellowing would continue up the plant.

It trimmed back the yellowing leaves and stems. It looks like it is indeed beginning to move up the plant. Any suggestions? Thank you!

I don't know where you are but if you are like us we are in a drought....drought will cause that yellowing. You can either water a lot and deeply and often or you can let things be and wait for rain. If you start to water, you generally have to continue. If you have plenty of water, go for it. If you don't and are living on a well, I wouldn't advise it.

I would still try some epsom salt (one tsp per foot of plant well watered in) or at least a compost tea since you only have two plants just in case. Were there tomatoes in the same spot last year? I've gotten to where I don't trust anyone elses seed saving or plants (because of crosses in open pollinated varieties and disease) and now grow almost everything from my seed and potting soil.