Write your hypothesis in a way that reflects this. You could say plants are harmed by more than 12 hours of sunlight or that plants need at least three hours of sunlight, etc. You will conclude that the results are either significant or they're not significant; they either reject the null hypothesis if P is below your pre-determined significance level or don't reject the null hypothesis if P is above your significance level.
In this case, the null hypothesis is simply that the treatment or change will have no effect on the outcome of the experiment. For example, if your null hypothesis is that plant growth is unaffected by duration of sunlight, you could state the alternate hypothesis in several different ways.
The null hypothesis might really be true, and it may be that your experimental results deviate from the null hypothesis purely as a result of chance. You should also give either your raw data, or the test statistic and degrees of freedom, in case anyone wants to calculate your exact P value.
She has taught science courses at the high school, college, and graduate levels. The probability of getting 17 or fewer males out of 48, under the null hypothesis, is 0. You may be wondering why you would want to test a hypothesis just to find it false.