When to transplant perennials

(Question)

I had to have a fence rebuilt along one side of my garden last fall, and on your advice I moved a number of perennials that were next to the fence temporarily to another part of the garden. I didn’t think they should be moved back until the fence was stained (it had to overwinter before staining until the nighttime temp was at least 12) and this has only just now been done. I would like to move the perennials back but they are now quite large. Is this a bad time to move them? When should I do it?

(Answer)

It is good that you waited to move the perennials; they survived quite well. As I do not know what perennials you have to move, some will move well enough now, yet others might prefer the fall.

Although we have been receiving a spate (although we waited a long time for it) of hot weather this last week, we are still in May and things can be moved, as long as you prepare a proper hole with added compost and are willing to water regularly and deeply to help establish the roots. Transplant fertilizer may help – it comes as a liquid that you mix with water according to instructions. The numbers are usually 5-15-5; the middle number is high in phosphorus, which helps the feeder roots to grow.

I would prepare the holes first before digging out the plants (re-sizing  the hole can be done when the plant is dug out of its current location). The less the feeder roots are exposed to wind, and heat, the healthier they will be when transplanted. If the soil is very dry around the plant, you should put the roots in a large bucket  or trug and fill with water to thoroughly wet the soil around the plant. If you have a plant like a hosta, and it is large, you can split it with a spade and create more hosta at this time. If you have irises or peonies, these should be let go till late summer, and transplanted then.

Put water in the hole you’ve chosen for that plant and place the plant in the hole and check for it being level with the original soil line. You may have  to adjust with more or less soil in the hole to be sure that the plant is level with the soil line. Press the soil around the plant to remove large air pockets, then water thoroughly with the transplant fertilizer. You can mulch around the plant to maintain moisture to a level of about 10cm to 15 cm. Be sure that the mulch does not touch the plant itself, as it could retain too much moisture and encourage fungal growth.