Tulsi can also thrive inside in winter months if kept in warm place free from drafts. Put in front of window on south side of house (if available) and allow for sun as much as possible. This can be done, but it is true that warmer summer months make it easier.
Tulsi is a sacred plant and should be worshipped. The scriptures point out that one who cultivates Tulsi with love and devotion will receive great spiritual benefits. This is more than true. There should not be any chemical fertilizers used on Tulsi. Use cow manure instead. Water to keep soil moist at all times, but be careful of too much...esp in winter when the moisture isn't drying out as well and can become to damp, clamy, and allow mold to grow. This would be bad to Tulsi. Offer Tulsi water daily, even if just a little spoon.
Arati, Tulsi pranams very good. Never pick tulsi leaves. If tulsi needs trimmed, or if leaves are desired for puja, you should clip with scissors. While making tea out of tulsi is something that is being done by some, this is NOT proper, or respectable to tulsi. Worshipping tulsi and offering her leaves in puja to Lord is what is proper. Tulsi's growth is many times proportional to your degree of love, and devotion to her.
There are many Krishna temples throughout USA who maintain tulsi plants on the alter of the Lord Sri Krishna. I was at the beautiful Hare Krishna community of New Vrindavan in West Virginia a couple of weeks ago and was impressed with the very nice tulsi cultivation there. If you find that tulsi it sick, perhaps more sun, more/less water, transplanting to larger pot, or even changing soil to create nicer and more richer mix of cow manure, and high quality potting soil will help. Hope this helps out. May Lord Sri Krishna bless you all. This edition to my previous message is to suggest use of plant lights to help out in winter, or low sun days. This is useful too.
Plant lights are found at plant, garden stores and provide a wider range of UV light that plants prefer. Even flouresent lights are good for this. In the Skanda Purana it is said "Tulsi is auspicious in all respects. Simply by touching, simply by remembering, simply by praying to, simply by bowing before, simply by hearing about, or simply by sowing this tree, there is always auspiciousness." Tulsi is Lord Krishna's favorite plant. Smelling the leaves of tulsi leaves offered to the Lord is very purifying. There are nice references to tulsi in the book "The Nectar of Devotion".
Namaste and Jai Sri Krishna! Tulsi should not be thrown out if she has dried up. Branches can be used to make kunti mala beads, japa beads, or counter beads (beads use to count japa rounds). If you wish you can bury tusli, but throwing out is not good. This is recommended if Tulsi has already left. I know of Tulsi plants lasting a few years. Do what you can to prolong her life. The power of bhakti is strong! I presently have two Tulsi plants and it is getting into winter where I am. I use plant lights and also make sure that she gets adequate sun light on the south side of house through a window. This is of course changable daily. Some "sick" plants were given to me and they too are doing well.
Letting small plants grow in a small planter until root structure is developed is a good idea. Sometimes having a planter much bigger than the plant isn't good. It may be better to gradually increase planter size as plant grows. Making sure to use cow manure for fertilizer is good. Dried kind from green house works, but stay away from chemical fertilizers. Use plant spray bottle from time to time to bath Tulsi and keep leaves clean. Offer water, ghee lamp, incense from time to time for nice puja and that will result in a much better condition beyond just the simplicity of water, light, and soil conciderations.
All is important. If she is not doing well, perhaps a change of soil, more/less water, more light, or cow manure to replenish soil will result is change back to health. Consider such conditions to be a test of how much you desire her to remain. Playing bhajans and the spiritual puja should not be underestimated though. Be careful about not enough sun, or too much water esp in winter. Water amounts should reflect show fast what you put in earlier is being used.
Over doing something good can also be bad. Yellowing leaves may indicate not enough light, or water amounts may need changed. Black leaves can be trimmed off with sharp scissors, never pulled. These are just some suggestions that I hope will help you. Hare Krishna
Dont Keep near to Glass window during winter.Window sill does give it some light and it growing vertical to reach that light , which probably mostly from top and not scatttered.
Most important thing is, that window sill become very cold during winter.Air near windows becomes cold when it comes in contact with glass. I have confirmed it by placing thermometer.
Please try to keep plant about a foot away from window. I actually had to remove my tropical plants further away and set up a "Plant growing light". Iturn it on for 3-4 hours a day. Thay are doing much better.