What to plant in the fall

Procrastinators, rejoice! It's not too late to plant perennials, trees, shrubs and other hardy plants. In fact, autumn is actually the best season to get many hardy plants into the ground. So if you've put off starting a new bed or missed getting those trees in last spring, you can still do so any time between mid-August and about six weeks before the first killing frost (in most of Canada, that means well into October and sometimes beyond). An added bonus: you can take full advantage of the fall plant sales at your local nursery.

Home gardeners are used to doing most of their planting in spring because of tradition. Back when the average flower bed was filled with annuals, this was the norm, as annuals are tender plants that only live for one season. When perennials came into the fore, the spring planting habit simply carried on. Yet most perennials (as well as many shrubs and trees) do best planted in fall; when plants go into the ground in spring, they're faced with cool soil that slows down their rooting, but soon have to cope with warm air temperatures that stimulate leaf growth and flowering. Then come the summer droughts, which further hinder root formation. As a result, many spring-planted hardy plants fail to root properly and spend their first summer looking stressed and scrawny. In contrast, fall-planted specimens go into warm soil at a time of year when, in most of Canada, rainfall is abundant and evaporation is low. This combination of warm soil and even moisture is ideal for root growth, which continues long into the season, well after the aerial (above the soil surface) parts of the plant are dormant.

Typically, a fall-planted perennial will reach its full size the first summer, while a spring-planted one can take two or three summers to become well established. Though the difference is less dramatic, the same holds true for many trees, shrubs and conifers.

It's often said that fall-flowering perennials are best planted in spring, but that's only partially true. If installed when they're in bud or bloom, their root systems may fail to properly develop (specimens that are blooming rarely have enough energy left for good root growth), leaving them more susceptible to winter damage. The solution is to simply shear the plants back by half to eliminate their bloom. They'll then settle in and root well. Fall-flowering perennials that can be treated this way include mums (Chrysanthemum x grandiflorum), Japanese anemones (Anemone x hybrida and others) and asters (Aster spp.).

And there you have it: planting in the fall is not only perfectly acceptable, it's the best time of year to get most plants into the ground. So pull out your shovel, do some digging and enjoy the fruits of your labours come spring.

Fall planting secrets
Dig a hole as deep as the plant's root ball and about three times as wide, amend the soil if necessary, add a pinch or so of mycorrhizal fungi for better root growth, then nestle in the plant, gently teasing out and separating some of its outer roots. Fill in with soil; tamp lightly and water well. Add a seven- to 10-centimetre layer of mulch, such as compost, shredded leaves or decomposed leaf mould, keeping mulch 15 centimetres away from the stem of woody plants and five centimetres away from the stem of herbaceous plants. This will help the soil stay warm, which provides a longer growing season for plant roots and prevents frost heave in winter. Water as necessary until the ground freezes—your goal is to keep the soil evenly moist, but not soggy, until the very end of the growing season.