Be your own dahlia expert and cure any problems promptly. But first you need to know what is the cause and the signs you might be experiencing on your plants. Leaves will tell you exactly what they are getting too much of or too little of, and what they would like you to do about it, as soon as possible!
Dahlia leaves should be dark green and healthy. Slight yellowing leaves, called chlorosis, on lower leaves of dahlia plants and leaf drop is caused by low fertility.
Chlorosis with tiny black dots on those slightly yellowed leaves means you have a low ph in your soil. If your soil range is below 5.8, it causes dahlias to take in too much iron and manganese, to toxic levels, collecting in the leaves.
Dahlia leaves that have burnt-dried edges is a sign of too much fertilizer.
Your soil could be full of all the right minerals but what determines the amount of those nutrients your dahlias can readily absorb is…Surprise, your soil’s ph level. Not really a surprise but to new gardeners just starting out with dahlias I want to make sure everyone knows the importance of your soil’s alkalinity and why horiculturists and dahlia farmer’s always talks about it. (Bacteria and fungi also help roots uptake nutrients.)
An excellent ph range is 5.8 to 6.2 and you should take steps to correct if above or below these numbers before your dahlias leaves start to show any unsightly symptoms.
On a ph chart scale of 1 to 14, 7.0 is considered neutral. Above that number is sweet/alkaline, 6.9 and below is considered sour/acidic alkaline. (Some days I feel sweeter than sour. It could be a result of what I’m eating.) Our soil here is slightly acidic.
Composted leaves and vegetable material may be worked into your soil. Peat moss is also good as it’s ph level is around 3.5 and is an organic product. Really I cannot say enough about composting and how this decayed-organic material helps plants thrive because you are feeding the soil, which in turn feeds the dahlias.
Many garden centers will suggest ground limestone to lower ph but I also want to tell you if you are an organic grower this is not allowed to become a certified organic grower by the state.
I heard that the most commonly tested soil is classified as extremely acidic, but that does not mean that yours will be. A soil test will give you the available ratio of Nitrogen, Phosphorous, Calcium, Potash, Magnesium and Sodium as well as your soil’s composition. Home soil tests kits usually only test ph and Nitrogen, Phosphorous, and Potash.
I am including a state by state link of more detailed soil analysis here. Let’s talk more in depth soil testing again later.
Until tomorrow…Enjoy your dahlias.