Growing purple yams

[teonanacatl]

I need help, some of my purple yams this year grew lots of shooting stems but not many tubers, and the bulbils and tubers produced are not purple. I'm wondering if they need two years from bulbils to produce tubers? Or if some suffered bug damage to the roots? Or perhaps some are not purple yams?

I did some keying whilst they were growing and they all keyed out to be Dioscorea alata, so I'm perplexed as to why the different growth. Pics attached.

Purple yam with good tuber development

Not purple yam, note the many shoots forming but limited tuber (there are multiple plants in this picture)

[alfamiller]

yams dont like alot of fertilizer or water ... m ine grow best untouched

[alfamiller]

yes they dont get purple till they are either big or old(1 or 2 years)

[theuserformallyknownasd00d]

Yeh prob too much nitrogen

[teonanacatl]

Ive grew yams in this bed last year and they were all normal purple yams. I dont fertilise, but I planted pigeon peas around the edge of the garden this year but doubt that has increased the nitrogen that much. The "purple" yams are growing intermixed with the other ones, so I guess it might be age.

[starling]

I've grown a few different types of yams, they're a great crop and a must-have for those into self sufficiency. The best I tried was a chinese white variety bought from gumtree, creamy and sweet.