September in the Boise Garden: Let’s think next Spring - 10 Things to Do Now for a Healthier Garden Next Spring
September is one of the most useful months of the year for Treasure Valley gardeners. The intense heat of summer is beginning to ease, but the soil is still warm enough for roots to continue growing. That makes September an excellent time to plant, transplant, improve your soil and prepare your landscape for the coming winter.
While it may feel like the gardening season is winding down, September is really a transition month — and there is still plenty to do.
Here are 10 things we recommend doing in your garden this month.
1. Keep Watering Your Trees and Shrubs
One of the biggest mistakes gardeners make in September is assuming that plants no longer need much water because temperatures are cooler. I stress this in most every article, but it’s one of the most important things you can do for your plants! Keep in mind that when winter sets in, your plants won’t get much water until spring as the ground likely will be frozen, keeping miosture from reaching the root system.
Trees and shrubs — particularly those planted this year — still need adequate moisture as they prepare for winter. Newly planted trees and shrubs should be watered deeply rather than receiving frequent, shallow watering.
Continue monitoring soil moisture throughout the fall, especially during periods of dry weather. Newly planted trees should continue receiving supplemental water until the ground begins to freeze.
Remember: A plant going into winter under drought stress is more vulnerable to winter damage.
2. Plant Trees and Shrubs
If you have been thinking about adding a tree or shrub to your landscape, September is an excellent time to do it.
Cooler air temperatures reduce stress on newly planted plants, while the soil can remain warm enough for root development. Fall planting also gives trees and shrubs an opportunity to establish their root systems before next summer's heat arrives.
Deciduous trees and shrubs can generally be planted well into fall, while evergreens benefit from being planted early enough to establish before winter.
At The Home & Garden Store, we always encourage homeowners to select plants based not only on how they look today, but also on their mature size, location and water requirements.
3. Divide and Transplant Perennials
September can also be a good time to divide or move many established perennials.
If a perennial has become overcrowded, is producing fewer flowers or has simply outgrown its location, fall can provide an excellent opportunity to move it.
Plants moved or divided in early fall have time to begin establishing roots before winter. Perennials planted in late summer or early fall should be kept adequately watered and may benefit from a protective layer of mulch later in the season.
4. Don't Stop Fertilizing Everything — But Know What You're Feeding
September is not the time to simply apply a high-nitrogen fertilizer to everything in the yard.
Your plants have different nutritional needs depending on their type, age and condition. Overly encouraging tender new growth late in the season is not always desirable as winter approaches. Our recommendation is to apply Ferti-lome “Fall & Winter” fertilizer in September and then again around the end of November. The late application will provide early plant growth next spring.
Instead, evaluate each plant and determine whether it actually needs fertilizer. This is also a good time to concentrate on improving the soil rather than simply adding more fertilizer. The Home & Garden Store/Aloha Home and Garden has an Idaho Certified Nurseryman that can help you with choosing the right products based on your location within the Treasure Valley, the type of plants you have and the type of soil.
Healthy soil is one of the best investments you can make in your garden.
5. Plant Cool-Season Vegetables and Herbs
Your vegetable garden doesn't necessarily have to end when summer vegetables slow down.
Cooler temperatures can be favorable for crops such as lettuce, spinach, arugula and other cool-season vegetables, although the remaining growing season needs to be considered carefully.
September is also a good time to evaluate which vegetables performed well this year and make notes for next year's garden.
If you're planting late-season crops, keep an eye on the weather and be prepared to protect tender plants when frost threatens.
6. Start Preparing for Frost
September is the time to start paying attention to overnight temperatures.
In Boise, the median first temperature of 32°F or lower occurs around October 18, according to National Weather Service climate data. A hard freeze of 28°F or lower has a later median date of about November 7. However, frost can arrive earlier or later depending on the year and your specific location within the Treasure Valley.
That means you still have time — but don't wait until the first freezing night to make a plan.
Keep frost cloth or other protective materials available for tender plants, and know which plants in your landscape are most vulnerable. We sell frost cloth by the lineal foot, so you can purchase the exact length you need.
7. Refresh Your Mulch
Fall is an excellent time to evaluate the mulch around trees, shrubs and perennial beds.
A good layer of mulch can help moderate soil temperatures and conserve moisture. It can also help protect plant roots from the repeated freezing and thawing that can occur during winter.
But don't pile mulch directly against tree trunks or shrub stems. Keep the immediate area around the trunk clear.
Think “donut,” not “volcano.”
8. Clean Up Diseased Plant Material
Fall cleanup is important, but don't assume you need to remove every leaf and piece of organic material from your landscape.
Healthy plant material can contribute organic matter to the garden. However, leaves and stems showing signs of significant disease should be removed appropriately rather than left in place to potentially contribute to future disease problems.
This is also a good time to make notes about plants that experienced disease or insect problems this year. Those notes can be extremely helpful when planning next year's garden.
9. Don't Cut Everything Back Too Early
It's tempting to look at a garden in September and start cutting everything down. Most plants store the nutrients back into the root system, so typically we recommend pruning some time after October 20th.
Resist the urge to do too much too soon.
Many perennials and ornamental plants continue to provide interest well into fall, and some seed heads can provide food or habitat for wildlife. Leaving certain plants standing until later in the season can also add winter interest to the landscape.
Instead of giving the entire garden a haircut, take a selective approach.
Clean up what needs cleaning up, but let the plants that still look good continue to contribute to the landscape.
10. Think About Next Spring — Now
Perhaps the most important September gardening task is simply planning ahead.
Walk around your property and ask yourself:
What worked well this year?
Which plants struggled?
Where did I have too much sun or too much shade?
Are there areas that need better soil?
Did any trees or shrubs outgrow their location?
Where could I add fall color?
What would I like to plant next spring?
September gives you a chance to make those observations while the growing season is still fresh in your mind.
11. Pumpkins, Straw and Mums Are Available – Now
We have your fall supply of mums, pumpkins and straw in both half-bales and full bales available at the nursery. Stop by today and let us help you with all your gardening needs.
One September Mistake to Avoid
If we could give Treasure Valley gardeners just one piece of advice this September, it would be this:
Don't assume your garden is finished just because summer is ending.
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