Should he trim these things partially all the way back, or just leave them on their own? The green portions look really healthy.
Leave them . Winter time , lucky you .
This happened to us a couple years ago. Suddenly our dead tomato plants we hadn’t bothered to clear in the back of the garden grew shoots and blossoms. We ended up with some nice winter tomatoes. (Los Angeles, I’m not sure where your son is.)
Tell him to leave them and see what happens.
Tomatoes are vines- they grow from the ends so don’t cut them off. What he can do if he wants to is bury part of the stem so the green part is sticking out of the ground like a new plant but leave it attached to the original plant until it grows new roots from the buried part of the stem. Then, after a month or so when new growth is apparent, cut it from the mail stem. I do this every year in Fall pto prolong my season here in So Cal. Whether it will make it until Spring depends on where in SoCal he lives and if it gets frosts there.
Tomatoes are what is called “weak perennials”. In the right climate they can grow for up to around three years, sometimes more, but usually get weaker each year and produce less. A strong, healthy plant may be diseased, but can fight it off with no problems, but as they start a new year, are weaker and the disease that formerly didn’t bother them, can take over. Also, the disease can then spread to other plants from the diseased one. That’s why commercial growers start new ones each year.
You don’t want tomato plants to touch the ground. This leads to disease, fungus, and insect problems. That’s why you use a cage to keep them off the ground. Also to keep them growing up, not out, since they will spread and take up more of the garden, looking unsightly, as in your pics.
Tomatoes that are heavily pruned can actually grow back better the next year. Even in harsher climates. Last winter was very mild in Southern NY where I am. I container plant dozens of plants (some years up to 150) and usually cut them back in the fall and let them die over the winter. Last year after I cut them back I dumped the root balls and dirt in a low spot in a corner of the yard. This year I had a huge mass of new tomatoes grow from the old roots. I had the same thing happen with some Thai hot peppers which I hadn’t even dumped after cutting back, and they were completely exposed to cold and snow in their large pots, which amazed me since they are such a hot weather loving plant.
I would cut back the plants to about 1 foot tall. Throw away or compost the old growth, and see if they come back in the Spring. They may not if the plants are weak. But if they have a strong root base, they may come back bigger, healthier, and produce much more tomatoes than if they are just left alone. Also, if they overwinter well, they will produce much, much earlier in the year than new plants do. Covering them with 3-4 inches of compost or mulch will help greatly in overwintering them.
By the way, with my hot chili pepper plants I cut back in the late fall, before frost, to around 6-10 inches, and re-pot them in small pots and put them in my basement or an unused room that doesn’t get too much light. And water once very week or two when they pots are dried out to around 2 inches deep. Then replant in large pots as soon as night time temps are in the high 40’sF to mid 50’sF, and the hot peppers grow insanely good the following year. Super hot peppers that have a very long growing season start producing within a few weeks of replanting in the Spring instead of late summer or even the Fall like the first year. I have overwinter hot pepper plants for up to four years before letting them die off so I could try new strains the following year.
Tomatoes are not all vines. They can be bush (determinate) or vine (indeterminate). Determinate means they grow to a ceratin size and produce all their fruit at once. while indeterminate means they keep growing and fruiting. The vine/indeteriminate can be cut back severely and grow. They do not just grow from the tips, but if severely pruned with grow from the base. As a matter of fact they are one of the few plants that should be buried deeper when transplanting than they were previously, as they will push out roots from the stem for a healthier and stronger plant.