Topping palo verde tree will lead to more pruning

Topping trees, harvesting potatoes and squash, and other gardening questions are on people's minds. Here are my answers to some of their questions:

Q: Is it OK to top a giant palo verde tree?

A: No. Before planting, you should have found a tree that will mature within the space allotted. Then it would require only minimal pruning.

To return your tree to your desired height, do a crown reduction to avoid destroying its beauty. Find a branch you want shortened. Come down to a subordinate branch and prune it at its crotch. All energy within the remaining branch now goes into the branch. Work across the tree until you finish. If you indiscriminately top branches, stored energy must go somewhere and activates all dormant buds on those stubbed branches to causes what we call witches' broom. You'll be pruning even more to remove these witches' brooms.

Q: When do we harvest our potatoes?

A: If you grow potatoes in mulch, it is easy to fish around to find the developing potatoes. Harvest them from baby taters to full size. Some varieties die down or wilt as potatoes mature.

Q: When do I harvest butternut squash? We left them until frost back east, but I think these are ripe.

A: You are right, they are ripe. They take about 100 days to mature and we're at that time. If they get overripe, they spoil quickly. Clip them off the plant when tan and keep in a cool dry place.

Q: What do I do with my tomatoes now they've stopped setting on?

A: This might scare the devil out of you, but cut them back to a foot high, making sure side stems branch off from the main stems. From these branching points, new growth will appear. In mid-September, and continuing through to Halloween, fruit will set on. At this point, pray for warm weather for them to mature. Last year, some gardeners were still harvesting fruit well into the next year.

Q: Where does the tomato hornworm come from?

A: I don't know why, but this is one of my most asked questions. Tomato hornworms are nocturnal so they do their business at night, which explains why you never see the huge, grayish moths that are about a hand-span wide.

Q: Will key limes grow in Laughlin?

A: I am sure you can in Laughlin, because Arizona grows citrus. Heat doesn't limit citrus production in Las Vegas.

Q: We put in a new drip irrigation system and are wondering the best way to fertilize our plants?

A: Nurseries sell fertilizer proportioners you attach to your system. They provide directions and sell a soluble fertilizer to use. Every time I water, my plants receive a small amount of fertilizer to keep them lush.

Q: Why did a two-foot hole along the side of my newly planted palm suddenly appear?

A: Most likely the hole was not filled properly and a pocket developed. Irrigating settled the soil, and the soil on top sunk. Refill with sand.

Q: Why are fronds on my newly planted Mediterranean palm turning yellow?

A: It's expressing a need for iron, zinc and manganese. These nutrients are packaged in a fertilizer called "palm food" and will green them up.

Q: I filled the water basins surrounding my trees with four inches of mulch. Will it be OK to cover the mulch with decomposed granite?

A: I don't know why you need to do this. An organic mulch is significantly cooler than rock. Besides, microorganisms are busy composting the mulch to improve the soil environment for your trees. When I pull mulch back that has covered the ground for years, I always find rich black soil and happy microorganisms and plants having a heyday.

Q: How do you tell when to harvest citrus fruit?

A: Watch the fruit closely. When it stops enlarging and reaches the desired size and color, it's time to enjoy. The final test is tasting.

Square foot gardening

Gardening is on the rise for homegrown vegetables. Learn more about square foot gardening. It's simple, versatile and adapts to all levels of experience. You'll use 20 percent less space, save time, water, work, money and heavy digging. Learn more about this new approach at 8:30 a.m. Aug. 7 at the Springs Preserve, 333 S. Valley View Blvd. Call 822-7700 to register for the class.

Linn Mills writes a garden column each Sunday. You can reach him at linn.mills@ springspreserve.org or call him at 822-7754.