Why are my pelargonium cuttings going black at the base?
This sounds like Blackleg which is unfortunately a common problem with Pelargonium cuttings. Its caused by a micro-organism which is spread by using unwashed pots/trays or tools. Using water from a source other than mains water can also cause this.
The only way to prevent it is to sterilise everything the cuttings will come into contact with - pots, trays, secateurs etc. Make sure you use sterilised compost from your local garden centre and it wouldnt hurt to dip the cuttings in a rooting hormone which contains a fungicide too. Make sure the soil isnt too moist as the disease will thrive in these conditions.
Dispose the affected cuttings with normal household waste to prevent it spreading.
Plants and gardens have always been a big part of my life. I can remember helping my Dad to prick out seedlings, even before I could see over the top of the potting bench. As an adult, I trained at Writtle College where I received my degree, BSc. (Hons) Horticulture. After working in a specialist plantsman's nursery, and later, as a consulting arboriculturalist, I joined Thompson & Morgan in 2008. Initially looking after the grounds and coordinating the plant trials, I now support the web team offering horticultural advice online.