Answer: Impatience do best in a rich, moist soil and prefer partial shade. There are a number of possible reasons this might happen. Did removing the trees allow more sun to hit the area where the impatiends are planted? If so, it may simply be to sunny for them.
It is possible that a heavy mulch of wood chips would temporarily "ties up" the available nitrogen in the soil and "starve" the impatience. A very fresh (green wood) mulch can also give off gases which are harmful to plants; generally mulch should be about a year old before you use it. Finally, if there was a black walnut tree in the mix it could be harmful to other plants due to a substance contained in the black walnut called "juglone".
Yet more possibilities would include that the pine roots may have moved into the planting area for your flowers and are robbing the soil of water and nutrients. If this is the case, you may have to plant them in containers. Another is that the pH has drifted and the soil has become too acid for impatiens or that the soil has simply become exhausted over the years. To find out, you'll need to run some basic soil tests. Your County Extension can help you with the tests and with interpreting the results -- the answer might be as simple as adding a bit of lime or working in some other soil amendments, but without a test you won't know for sure. (Their telephone number is 350-2540.)
Good luck with your impatiens!
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