Answer: Although a very tenacious plant once established, the ivy (Hedera helix) may have suffered during the drought and then become further dried out during the winter months, thus causing excessive winter damage. Newly planted evergreens are particularly susceptible to this because they have not fully rooted, and if allowed to become overly dry may even die.
With luck, they should come out of it so be a bit patient and hope for new growth to come out and replace the old damaged foliage. Make sure the soil stays evenly moist yet not sopping wet while they are becoming established, meaning at least the first full year and since these have suffered, I would suggest keeping an eye on the moisture for another full year. After that, they should not need watering except in cases of prolonged dry weather during the next few years and ultimately, should be very drought tolerant.
To help keep the soil more evenly moist, mulch around them with several inches of organic mulch such as shredded bark. This will help maintain soil moisture, moderate the soil temperature and also keep down weeds while you wait for the ivy to fill in. An additional benefit is that it will help feed the soil as it rots down over time.
Finally, to give them a boost, you might apply a layer of compost to the soil and/or a complete fertilizer such as a granular 10-10-10 according to the label instructions. Put this down so it is in contact with the soil and then apply the mulch.
Good luck with your ivy.
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