I have just now got a couple of rows of carrot seed in using one of those seeder dispenser things with a long plastic spout. When it arrived I opened it up and saw that it had enormous holes taken that I had carrot seed in mind. But after thinking about it, I realized that the smallest hole could be closed down to nothing if required. So with this hole only partially open and tapping the side of the planter, it is easily possible to place seed one by one as needed, sometimes giving a little help along with a small screwdriver. It recent months I have seen posts about the various and sometimes expensive aids, so just wanted to put my opinion of these particular ones out there for anyone interested.
