You are asking about transplanting a clematis and hosta during the summer. Yes, you can successfully move both of these plants from your old garden to your new garden if you water well the day before and then dig up the root ball and set it on an old sheet. Wrap the sheet around the root ball to keep the soil around the roots. Replant into a hole already dug with moist, amended soil. You are correct in that this whole transplant operation will have a better chance of success if you do the dirty deed on a cloudy day and in the evening. Protect the plants from the hot sun for a week or so after the move. Hosta are very easy to transplant, even in the summer. The clematis may struggle for a year after the move. You can shorten the vines of the clematis before you dig it up to make the plant more manageable to handle. Cut all the vines to 3 feet tall and keep the roots moist after the big move. You may lose flowering this summer, but the clematis will make up for it next year. Keep growing, Marianne Binetti