While pot-grown plants can be planted any time of the year, planting in mid-summer can be challenging, with dry soils and wind making establishing plants difficult. Planting in winter has its own struggles, mainly with not really wanting to go outside, but also with cold soil leaving roots sitting in heavy soggy conditions.
Spring is great, as top growth is minimal, allowing the plant to grow in balance with newly developing roots as the soil warms up. This balance – of root growth to top growth – is key to successfully establish perennials for a long, happy life.
But we’re not in spring. Autumn is the second best time to plant, as the soil is still warm and the rain has returned (admittedly not problem this year). Warm soil allows roots to develop and expand, making plants tougher and more resourceful more quickly. Autumn is actually the best time to plant early flowering perennials such as Pulmonaria, Brunnera, woodland anemones, Geum, and Peonies, which take advantage of establishing early, meaning you should get a good show out of them in six months rather than twelve.
Regardless of the time of year, when planting newly purchased perennials plants, it is important to plant them well to give them the best start. Tease out or break the roots at the edges of the root ball. This encourages the growth of new roots and ensures they grow out into the soil not back in on themselves. Remove any loose potting compost. If the plant is lightly rooted, having the roots come immediately into contact with the soil they’ll ultimately be living in is better than spoiling them with rich potting compost which they’ll complain about running out of. You can dispose of the top layer of potting compost as this is most likely to have weed seeds hiding in it, and mix the rest in to the soil you’re planting in. Dig a big hole. At least twice the size of the pot, but the more soil you loosen up the easier a time the roots will have establishing themselves. Fill the soil back in around the plant without compacting it (avoid stamping your feet around the ‘neck’ of the plant) and water well.
Nobody wants to hear the next bit, but the absolute best thing you can do for a newly planted perennial is: cut it back. In Autumn, most perennials plants are going to be as big as they ever get, or at least as big as they can be with their current root allocation. All that top growth demands a lot of energy and you have to bear in mind that plants in nursery pots have no competition; they can be confident of regular even watering by somebody paid specifically to do it; and as much light and nutrients as they need. Life in the real world is much harder, and less top growth means less stress, and more successful planting.
In nature, a plant will always balance its top growth with its root growth – or vice versa. This focus on root development, sadly, is something that gets forgotten about in the nursery trade. “Forgotten” being a euphemism for “is at odds with capitalism”. Typically, customers favour lush looking top growth, and the quickest way to achieve this is to grow plants indoors with rich compost and constant watering – the approach you take with cuttings, which have no roots. Where the plant is getting everything it could possibly want with no wind or stones or drought to contend with, top growth proliferates at the expense of roots, which are barely needed. You can produce and sell these plants quickly and they look great – until you plant them, when they flop and wilt.
Our growing area exposed to the wind rolling down the Dublin hills.
We like to grow things hard, outdoors, with lumpy compost that makes the roots work harder. This makes a plant’s transition to the ground that bit less traumatic. But it’s still no harm to cut them back!
1 Year later
2 Years later
So plant in Autumn. It’s a good time for many plants and not a bad time for the rest, and it’s always useful to understand why. Dig big holes, tease out the roots, and give your perennials the absolute best start for next year.