I noticed that too. I put 3 sw. potatoes I'd saved from last Thanksgiving in water on March 15, same time as when I started sprouting regular potatoes. Obviously, the reg. potatoes sprouted right away and were planted at the end of March. The sw. potatoes took forever to even show a bit of root (they were in the kitchen -- around mid-60's~70Ã‚ÂºF -- by a sunny window) I had them laying on their sides in a tub because I couldn't tell which was the sprouting end and which was the rooting end. Once the little roots started to grow (beginning of April) I stood them on their ends in water.
One variety called Hannah went in a large pickle jar, then, because it happened to fit, inside a quart size black plastic pot. The other one called Garnet was too fat and had to be put in a squat jar (no black pot sleeve). 3rd one called Jewel was a dud. NEVER rooted, never sprouted. Thinking they needed more warmth, I put the sprouting potatoes by a sunny window sill upstairs
where the temp is usually 4~8Ã‚Âº warmer and where I have a Seed Starting Area set up with holiday lights 24/7.
Hannah took off right away. The instructions I have said to plant the slips when about 6" long -- well Hanna started growing wild during the few days of 90Ã‚Âº heat wave we had (I refused to turn on the AC so it was at least mid 80's upstairs during the day and mid 70's at night) and sucking up all the water -- 1-1/2~2" every day. I started pulling off the slips and putting them in a separate jar of water and I now have at least 1/2 dozen slips growing roots and more sprouts growing! (I'll be lucky if I have room to plant 6 slips TOTAL) Garnet is still taking its own sweet time. Sprouts are about 2" long now. But I have at least 2 more weeks before it's warm enough for planting sw. potatoes.
I might try wrapping Garnet's jar with something black too. Otherwise, we're going to end up with mostly Hannah's, which is fine with me since that's my
favorite, but the kids' fave was Jewel, with Garnet close second, so I'd better grow some Garnet too!