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Thaumas P. Ehr, Landscape Architect

Fall Garden Preparation

Arizona's monsoon will soon be ending, bringing in drier air and a bit of relief, even though it will still be hot.

This is a great time for garden planning and preparation. Soon, you can plant cool-season vegetables and sow seed for colorful spring wildflower displays.

Mid- to late September and October is the time to begin planting in earnest, while the soil is still warm. The warm soil and lower temperatures are ideal for root growth, which gives plants a chance to become established before it gets really cold - usually by the end of November.

Here's how to prepare.

  • Sketch it out.

Start by sketching the layout of your vegetable garden, noting areas of sunlight and shade, also taking into account the mature size of the various plants.

Keep in mind that vegetables need at least six hours of sunlight. For wildflower displays, look for areas of full sun; many wildflowers do well in exposed areas where other plants might struggle.

This is also a good time to assess your landscape and plan for replacements of trees, shrubs and perennials that may have been damaged in summer storms or succumbed to the summer's heat.

  • Prep the soil.

Begin preparing the ground for your vegetable garden. Preparation is the same whether the soil has been previously worked or not. You must turn the soil to a depth of at least a foot.

If you are working a brand-new area with compacted soil, a rototiller might be useful to rent. Be sure to use a rear-tine machine for best results.

After turning the soil, work in an ample amount of compost evenly throughout - about 3 to 6 inches - and add fertilizer. Whether organic or off-the-shelf of the garden center, use a product containing nitrogen and phosphorus (e.g. ammonium phosphate 16-20-0), and use according to label directions. Mix thoroughly and rake smooth.

If you have soil that's too hard or rocky for digging, consider constructing raised beds, which will give you the advantage of building your own soil.

  • Plant vegetables, ready wildflower beds.

Cool-season vegetable seeds to plant in late September include beets, broccoli, carrots, cauliflower, kohlrabi, peas and many greens such as kale, spinach, cabbage, Swiss chard, bok choy and lettuce.

Herb plants (such as rosemary and lavender) and most vegetable transplants should not be planted until the end of September after temperatures are closer to 100 degrees; herbs and transplants can generally be planted through Thanksgiving.

Stagger the planting of seeds and transplants; then, if we have a hot spell, you won't lose everything.

You can also prepare your wildflower planting area now, although you won't sow the seeds until mid-October. If the area is compacted, add 2 to 3 inches of compost and manually work it into the soil.

If not compacted, add the same amount of compost on top of the soil and then seed the beds in October. If you have a rock top dressing, just throw out the seed and lightly rake in. If you have great soil, all you need to do is add the seed, lightly pressing it into the soil and watering in.

  • Fertilize other plants.

Vegetables and wildflowers aren't the complete fall story. Now is the time to give citrus their third and final nitrogen fertilizer application. (Remember: Valentine's Day, Memorial Day and Labor Day.)

This is also a good month to give your other plants their last light application of fertilizer for the year. Come October, it will be time to begin hardening everything off for the coming winter by letting up on the watering and ceasing fertilizer applications.

  • Winter lawn and cactus care.

If you must plant a winter lawn, stop fertilizing your Bermuda grass now in preparation for overseeding with winter ryegrass when night temperatures drop below 65 degrees.

If you don't overseed, continue fertilizing to keep your Bermuda grass green through most of November.

The sun's angle is changing and becoming lower. Watch for yellowing on your cactus and succulents through September and the beginning of October, covering with shade cloth if needed until mid-October.

  • Keep watering.

The heat is still on. Do not consider cutting back on watering until temperatures begin to show signs of dipping below 100 degrees and the nights begin to cool a little.

We are very fortunate here in the low-desert areas. We enjoy two planting seasons while most areas of the country experience only one.

The monsoon exit means it will be almost cool in the mornings, the perfect time to get out into the garden after spending the summer peering at heat waves shimmering off the sidewalks!

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