Question: Can a non-Jewish gardener come as usual on chol hamoed?
Answer:
Gardening is generally forbidden on chol hamoed (c.f. Shulchan Aruch Orach Chayim Siman 537, where various agricultural tasks are discussed). The exception to this is dovor ho’oved – i.e., a task that is performed in order to prevent loss (ibid Se’if 1).
In a situation of dovor ho’oved it is permitted to perform the necessary tasks in the regular fashion – i.e., without a shinui.
Additionally, one may not ask a non-Jew to perform any melocho on chol hamoed that one may not do oneself (Shulchan Aruch Orach Chayim Siman 543 Se’if 1). However, in a situation of a mitzva, it is permitted to ask a non-Jew to perform a melocho (Mishna Berura ibid s.k. 1).
Therefore, a gardener should not work on one’s garden on chol hamoed. If a specific situation of dovor ho’oved presents itself, a sheiloh should be asked.