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Great Gardening by Sally Cunningham: The season may be waning, but it’s not over

Two distinct thoughts washed over me this week as I walked around Buffalo and spent time in my own garden: Gardens change a lot throughout August. Early September gardens have lost much of the pristine prettiness of July, when daylilies bloomed and midsized plants were just opening. Many gardens are not tended as carefully as they were during the gardeners’ early love affairs with summer; some gardens have brown leaves, dead stalks and some large weeds. On the other hand, many gardens are just peaking – or would be if given half a chance. They are bursting with full-sized dahlias, Rudbeckias, asters, cannas, Japanese anemones, monks’ hoods and coneflowers. And it’s impossible not to notice tomatoes or hydrangeas just hitting their strides.

For people who keep their gardens going, there is no better gardening time than now.

So it is up to you: Consider the season over, and it will be over. It is a self-fulfilling prophecy. Or, tell yourself you have a month of gardening time (at least), and it will be so. You will have comfortable, cool weather to entertain – picture supper or brunch in your garden, surrounded by exuberant flowers. And you can get so much done to prepare for an even better garden next year. The secret is this: Just don’t quit.

Having advised you to keep on gardening, I must now clarify what exactly gardeners can and should do in late summer since I hear many questions that reveal some confusion.

Transplant, plant or wait?

I think we get in a lot of trouble because of old-time gardening advice in our brains. Long ago folks were taught to plant or transplant mostly in spring, and they miss a great opportunity to renovate a garden in early autumn or even in summer. The plants that are available in responsible, professional garden centers and nurseries are much different than the root-bound, overgrown summer leftovers of yesteryear – mostly. You will rarely see pathetic perennials begging for mercy in their six packs or 3-inch pots in August. The better professionals “pot-up” perennials and woody plants as they crowd their pots and water them well throughout the season. (This is not easy to do perfectly all season, nor are all situations and employees perfect – so do check the root conditions of your plants.)

Also, plants are now sold in larger pots than in former times. The summer perennials on the shelves should have good root systems and ample growing medium around them so their transfer into your garden soil is not shocking – as long as you remember to water appropriately until the ground is frozen.

Similarly, you can transplant or divide most plants successfully during the second half of the season, as long as you move a large mass of their roots and plant properly into compost-rich and well-drained soil – and, again, water. Whatever you plant or transplant must have the opportunity to grow roots outward and must never dehydrate.

How late is too late? A lot depends upon the ever-surprising weather patterns, but in our region it is generally safe to plant herbaceous plants (perennials) throughout September, the risks then increasing as time moves on. Trees and shrubs can be planted much later. They are going to go dormant and freeze in their pots in a nursery anyway, so they may do perfectly well – or even better – if you plant them carefully any time in October or November. Exceptions might be a marginally hardy plant (a Japanese maple on a hill in Colden) or some evergreens in exposed sites where winter winds dry them. Trust your professional CNLP or arborist whether you can plant late and protect such plants through winter, or if a spring job would be less risky.

When to fertilize or add compost

The compost answer is easy: Add it any time, whenever you prepare a new bed, plant or transplant, or top dress existing plants. Finished compost improves the texture and life of your soil, and does not burn or force inappropriate growth. This is a good time to use up the heavy drawers of your worm-bin (vermiculture) compost or the bottom, most finished half of last year’s compost pile. Or buy some. If you are going to spread fresh mulch before winter, put down some compost first – under the mulch – to support soil health.

The fertilizer question is more complicated. Another old gardening rule – still mostly right – is that you shouldn’t fertilize perennials or woody plants (especially with nitrogen) after early August because doing so would stimulate top growth instead of root growth. We want the plants to stop using their energy to produce new leaves and shoots. Instead, they should grow some roots and soon prepare to go dormant. Generally, true.

The exception? I have struggled with this and asked some arborist friends and nursery associates, concluding that some stressed trees and shrubs this summer simply needed a fertilizer boost later than normal. I have seen many chlorotic trees (leaves pale or yellow, smaller than normal), especially in pots, in poor soil, or recently planted. In part this is due to the odd weather pattern early in the season that included an extremely wet month, during which existing soil nutrients were washed through the root systems, and then extremely dry periods when the plants had no water to carry nutrients. So I did fertilize some stressed pots or recent plantings even in August, because they need leaves for photosynthesis to provide nutrients for the whole plant.

Container plantings – tropicals and annuals – and the houseplants outside for summer vacation should all be fertilized regularly. This is their time to flower and grow and look their best – and they depend completely on you.

Your September garden can be as beautiful and satisfying as you choose to make it. Don’t give up just because the kids are going back to school. It’s our time. And do pull a few weeds while you’re at it.

Sally Cunningham is a garden writer, lecturer and consultant.