I am growing some basil from seed on my kitchen windowsill. It came up really well and was looking really good until a couple of weeks ago. I have thinned to the stronger seedlings, tried watering and then leaving (not sure about watering so tried over and underwatering) but to no avail. Anyone got any tips?

They like plenty of heat and it did turn a bit colder a few weeks ago. They also don't mind plenty of water but I would say the problem is the cooler temperatures.

I have this issue everytime I grow basil. Let the soil dry out before you water. Are you using fresh soil? is the pot large enough?

Hi Buckaroo
Basil has one key requirement - sunshine! Position it in a protected full-sun position, and if this is not possible, grow in a moveable container. Soil should be well-dug and well-drained
In April, sow three seeds to a small pot in normal moist potting compost. Lightly cover with compost and place in a warm (15C or 60F) dark position - try and keep the temperature as constant as possible, never letting it drop below 10C (48F). The seedlings will emerge in two weeks time and the plant should be placed in a sunny warm position. Basil hates water on it's leaves and stem, so water from below.
Other than sun, basil has few requirements and can be planted outside as soon as the temperature reaches 10°C or more mid-May time normally.
Pinch or cut the leaves off as required, but always from the top. When the plants begin to produce flowers, pinch those out as soon as possible to encourage more leafy growth.
Fresh basil is by far the best for flavour.
Container Growing Basil
Basil is ideally suited to container growing in normal potting compost. Water regularly (from the base if possible) and feed twice a month with liquid plant food. As the season progresses, move them round the garden to the sunniest and most protected position. Basil will grow well indoors on a sunny windowsill. Although it is now mid May you can still sow seeds. Hope this helps cheers Pendelli