I have 2 evergreen magnolias that were planted last summer that so far this spring look awful. the once beautiful dark green leaves are a pale yellow/green and many are dying or rusty looking. I fertilized about a week ago but haven't seen any change so far. My yard is very heavy clay but I did dig out quite a huge hole and replaced the soil with topsoil/compost and bone meal. Is there hope that these will bounce back and green up once the rain subsides? What else can I do?
First - evergreen does not mean forever. Eventually, all leaves are shed/dropped and they will lose some of their dark green color. But these leaves should be the inner/older leaves. The outer leaves should not be falling off. Is the dark brown on the underside of the leaves? If so, this is indumentum and is perfectly normal. Some varieties of M. grandiflora have more indumentum and some are bare. Having said all of that, I suspect that, even though you have replaced the clay soil, you have created a tub which holds the water in the replaced soil and the roots are suffocating in wet soil. I would suggest that you replant the tree approximately 1 ft higher so the roots will be able to drain and breathe. But, for a couple of years while the tree is becoming established, ensure that the tree is well-watered while putting on new growth and when nature is not providing rain. Just do not leave the roots sitting in mud. Lastly, cover the area around the trunk with about 3" deep of bark chips to buffer the root area from the hot summer sun. I do not believe that you said where you are living. If what I have written does not appear to properly identify your situation, please let me know. It can be difficult to judge a situation over the internet. Good Luck.
Yes, never plant in an area of different soil unless it is big enough to accommodate the entire potential rooting area of the plant or is above the existing soil. The most common nutrient deficiency here is nitrogen, this becomes less available during the low temperatures of winter so yellowishness may appear at that time more so than others for that reason alone. Try to find out about having your soil tested to see what may be going on, down here you could ask your state Cooperative Extension Service about this - don't know what is available from agencies up there. If the trees got too wet over winter and started to experience root suffocation that could also produce effects to the top you may be seeing. However, poor color on southern magnolia and similar hot climate broad-leaved evergreens is frequent here and I think due primarily to nutrient deficiencies. Your trees will not be attractive until whatever the problem is becomes identified and corrected. Note in particular that a plant may have a nutrient deficiency and still be quite green, when one gets to the point of becoming yellowish it indicates a severe situation.
