How late can I plant?

The big plant sell-offs with drop-dead discounts are on now and every gardener wonders the same thing. Will buying plants in the fall really save money or is it false economy to shop for plants in September?

If I was a meteorologist, I could answer the question of "how late can I plant?" with more accuracy. however, I'm a gardener and can only speak for the plants.

Here are five reasons why late plants don't transplant well, one thing you can do to help the survive and a list of plants waiting for you to buy them right now. 1. Perennial plants start to go dormant now, even if they are still in pots. This means they are not initiating new roots and probably won't grow out and into the soil. Plants with fleshy roots – such as peonies and monkshood - are the exception. They will survive dividing and fall planting better than most other plants.

2. Weather is variable in the fall. I remember years when branch-breaking snow collapsed new and old plants alike and left the garden showered with green leaves and dead trees. Any erratic fall weather that strips off living leaves and branches could adversely affect new trees because they don't have as much energy in reserve as established trees do.

3. Irrigation systems are turned off. Companies start contacting homeowners in early September to shut down irrigation systems yet because of variable weather (see No. 2), we never know if we should expect flood or drought. If you do turn off your irrigation, do not stop watering if it is dry. New and existing plants need water and green plants lose water through leaves as long as they have them.

4. If you do buy and plant perennials and woody plants now, protect the roots with a four centimetre layer of mulch so the soil doesn't freeze as fast, stays more evenly moist and is protected from freeze-drying winds during winter. Mulch will also prevent the plants from frost heaving or from popping out of the ground during freeze and thaw spells.

5. Some plants go in the ground dormant and start to sprout in the cool fall air. These are the vegetable bulbs such as garlic, large ornamental bulbs such as tulips and lilies and small bulbs like grape hyacinth and squill. You can plant these now because no matter what happens above ground this fall and over winter, these will bring a beautiful welcome to the spring garden. Use the old pointy-side-up rule and cover bulbs with at least double the depth of soil to the size of bulb. A garlic clove that is 1.5 centimetres long will have three centimetres soil on top while a five-centimetre tall tulip bulb will be covered with 10 centimetres of soil.

Planting now has its risks, and the benefits of buying late in the season are only worthwhile if the plants survive. But then again, there are those deep discounts.

Donna Balzer is a garden writer and speaker. Check out her blog at www.gardenguru.net or follow on
twitter @NoGuffGardener.