My lemon tree has yellowing leaves. I think it needs repotting but I don't know the best soil to use in the repotting and what special feed.
If the leaves are green veined, but yellow else where, the plant has a iron deficiency. This article will help fix that: https://www.gardeningknowhow.com/plant-problems/environmental/leaf-chlorosis-and-iron.htm These articles will help you with fertilizing: https://www.gardeningknowhow.com/edible/fruits/citrus/fertilizing-citrus-trees-best-practices-for-citrus-fertilizing.htm, https://www.gardeningknowhow.com/edible/fruits/lemons/learn-about-fertilizer-for-a-lemon-tree.htm They also prefer well-draining, slightly acidic soil. Here is some help for its care: https://www.gardeningknowhow.com/edible/fruits/lemons/growing-lemon-trees-containers.htm
When I cut my lemons open, they have a brown mark all the way through the center. Just wanting to know how to get rid of it.
It sounds like you have an problem with Bronze Orange bugs. They cause damage to citrus fruit like that. Here is an article that will help you with them: http://gardenclinic.com.au/bug_watch/bronze_orange_bug/
I have a lemon tree about 6 yrs old. It never has produced lemons. Do I need another lemon tree for my plant to produce lemons? If so, can I grow a plant from a clipping from my tree or do I need another tree?
You do not need another lemon tree to produce fruit. If it was grown from seed, it may not be old enough to bear fruit. They need 3-6 years to reach fruit bearing maturity. Have you fertilized? Nitrogen encourages leaves to grow, but not fruit. Too much can actually keep a plant from producing fruit. This article has information on how to fertilize your trees: https://www.gardeningknowhow.com/edible/fruits/citrus/fertilizing-citrus-trees-best-practices-for-citrus-fertilizing.htm I would also try giving it some phosphorus rich fertilizer like bone meal. If it is lacking phosphorus, it will not be able to produce blossoms (which means no fruit.). If you have not read it yet, this article may also be helpful: https://www.gardeningknowhow.com/edible/fruits/lemons/lemon-tree-not-fruiting.htm
How long will it take to grow a lemon plant (when potted with seeds)? I planted some seeds of lemon in a pot a week before and just wanted to know how many weeks will it take to appear or the when will I get the results?
It will take perhaps one or two weeks for the seeds to sprout. After that, the length of time it takes to grow into a plant depends on how big you want it to get, how you treat it, what variety of lemons you're growing, among other things. This article will help you grow your seeds into a lemon plant: https://www.gardeningknowhow.com/edible/fruits/lemons/how-to-grow-a-lemon-tree.htm
My lemon tree looks beautiful. I've had it for two years, but it won't flower or fruit.
This article should answer your question: https://www.gardeningknowhow.com/edible/fruits/lemons/lemon-tree-not-fruiting.htm
My lemon plant gives fruit in winter, not in summer. How can I get in summer?
The times for lemon fruiting depends on your climate and variety. In warm climates, some lemons may actually produce year round. There are many types of lemons, with true lemons thought to be Eureka (spring fruiting) and Lisbon (summer fruiting). If yours in fruiting in winter, you likely have one of the winter-bearing types - Meyer or Ponderosa are common ones.
I cannot get a lemon tree to survive. They keep dropping all their leaves and then the branch dies. At first I thought it was because the sprinklers hit the tree, but I am not sure.
Lemon trees, like most citrus, need lots of water and good soil to grow. These articles should help you with growing lemons: https://www.gardeningknowhow.com/edible/fruits/lemons/how-to-grow-a-lemon-tree.htm, https://www.gardeningknowhow.com/edible/fruits/lemons/growing-lemon-trees-containers.htm, https://www.gardeningknowhow.com/edible/fruits/lemons/learn-about-fertilizer-for-a-lemon-tree.htm, https://www.gardeningknowhow.com/edible/fruits/citrus/tip-on-water-requirements-for-citrus-trees.htm