In May I planted some grapefruit and lemon seeds pretty much on a whim (basically seeds + dirt + water). 3 of 4 grapefruit sprouted but only 1 lemon out of 8 (must have got something wrong), and he doesn't seem to be growing as he should.

The seedling was repotted into Citrus compost (as with all my other plants). A second pair of leaves arrived quickly, but in the last 6 weeks there has been no growth at all. I'm tempted to re-pot into fresh compost and check the roots but to be honest I don't know what I'd be looking for anyway. The leaves aren't changing in colour. Everything is fed with summer citrus feed and watered when the top half inch or so of compost is dry. They get plenty of sunlight through the window they sit by. I'm in Cornwall so they can't live outdoors all the time.

The lemon is on the left in the pic below (the other 2 are grapefruit of the same age).



Any help would be gratefully appreciated.

On the upside, this is the grapfruit that sprouted first, a good 3-4 weeks before the others, and he's coming along well so fas as I can see:

I don't see anything wrong. Grapefruit are about the fastest growing of the citrus. Give the lemon time. Citrus grow in cycles... The roots will grow & then you will see a flush of leaves, then back to the roots and so on...

Six to eight weeks between the first true leaves and the next set of true leaves is about the correct amount of time. After your lemon seedling germinated and grew it's first pair of true leaves, the tree needs to develop a larger root system, before it can produce and support additional above ground foliage. Welcome to the forum, we are excited that you have become a member. - Millet

Plow - Plant - Fertilize - Harvest - Repeat

Thanks for the reassurance, I was worried by the comparative lack of growth and lighter colour on the leaf edges (which isn't extending or receding at all). So long as he looks OK I'll just keep doing what I've been doing.

I'm going to buy a couple more lemons tomorrow and try again with the seeds to see if I can get a better than 12.5% germination rate, I think the last ones were kept too wet. The basic compost I used went from powder to sludge in an instant.

I'd love to do a lime as well but all I can find in shops in the UK are seedless ones rather than key limes.

I got seeds for lime plants from tradewinds they can send to the UK, about 25% germinated