This is on several of my tomatoe seedlings, what am I doing wrong?
Thanks in advance!
Looks like a magnesium deficiency if they are all on the lower leaves. Young tomato plants often show deficiencies, so may not be an issue. There can be several causes, and maybe more. You'll have to determine why.
1. Fertilizer that lacks magnesium such as Miracle Gro, if you are using an inert medium. Epsom salts or dolomite lime might help depending on pH.
2. pH problems. High pH especially will lock out magnesium. High water pH can cause this.
3. Calcium/magnesium imbalance. Too much calcium can lock out magnesium. Hard water can also cause this.
4. Overwatering can cause uptake issues.
5. Over fertilization can cause lockout of magnesium.