Q: You mentioned that male asparagus plants produce more than female asparagus plants. How do you tell the difference?
A: Male asparagus plants produce more spears than female asparagus plants because of the energy needed to produce seed by females. So male asparagus plants are preferred over female asparagus plants. You pay a premium price for all-male asparagus crowns or roots.
We call plants that have male and female forms “dioecious.” The plants and spears look identical. The flowers are slightly different.
Male flowers and female flowers are easy to sex in some plants. Flowers of asparagus are not. Male and female asparagus flowers look nearly identical.
Asparagus spears are harvested for eight to 10 weeks in the spring. Then the spears are allowed to grow into 5- to 6-foot tall bushes called “ferns.” These ferns produce small white flowers that are either male on the male plants or female on the female plants.
The female plants produce round berries. The male plants do not.
The easiest way to tell the sex of an asparagus plant is to look for the berries that form from female flowers on the ferns. Dig up and remove the entire female plants, including their underground crowns. Do this before these young green berries become red in color or mature and can spread seeds in the garden.
When you buy 1- or 2-year-old asparagus crowns (roots) for planting, the more expensive ones will be labeled “all male.” To get all-male plants, someone must “rogue out” or remove all the female plants, including the crowns.
Q: My 30-foot-tall live oak tree is covered with aphids. Should I spray now, or will the aphids die if the weather gets cold?
A: Aphids overwinter at the base of trees and weeds nearby. Their populations are much smaller, but they are there. Eliminate weeds and apply dormant oil to the tree twice — once in December and again in January before new growth begins.
Dormant oil is a holdover name from decades ago, when forms of this oil were safe to apply only during the winter. You might find this product now with names like horticultural oil, superior oil, supreme oil and others.
These newer oils are different. These are not vegetable oil or neem oil used as insecticides but a different type of oil that smothers overwintering bugs. I have used these newer oils in the fall, spring and even early summer months as long as the plants are not flowering.
Ants and aphids rely on each other. Controlling ants helps control the spread of aphids and keeps them in check. Controlling ants when aphids are problems is an important component when controlling aphids. I like to use ant bait products such as Amdro applied exactly as the label says.
Don’t worry about small numbers of aphids on trees if you eliminated weeds and controlled their ant buddies. Leave them alone unless there is some problem you can’t live with.
If the ant problem is intolerable, apply soap sprays, neem oil or a systemic insecticide if it’s a bad problem. But don’t go in that direction unless you must.
Q: We have a Meyer lemon and Bearss lime in clay pots. The pots are deteriorating, and the trees should be replanted into other pots. In the desert, what time of year is best to transplant these trees into new containers?
A: Put fruit trees into new pots in late winter or the beginning of spring. In our Las Vegas climate, this would be from mid-January until sometime in February. Bearss lime is sensitive to mild freezing temperatures. Meyer lemon tolerates cold temperatures better.
If they are kept outside, wait until the coldest weather of winter has passed before repotting them. Plants growing in containers or pots need their soil refreshed or the plant repotted every three to four years to prevent a slow decline in health.
Replanting, or repotting, is not difficult if the containers and plants are relatively small; the plant is gently eased from the container, roots and soil around the edge of the root ball is shaved off, and the plant is placed back into the container with fresh soil or container mix surrounding the rootball.
If plants are large, the soil still needs to be refreshed every few years. Perhaps one way is to auger vertical holes throughout the rootball, while still in the container, and backfill these holes with new soil mix.
Auguring holes into the rootball damages plant roots, but the old container soil must be refreshed. Another method is removing the root ball from the container, removing old soil with a strong stream of water, pruning some of the roots and repotting it.
Prune the top back when finished to compensate for any root damage during repotting.
Q: When do you harvest butternut squash?
A: Butternut squash, a winter squash, should be fully mature before it is harvested. Knowing when to harvest comes from experience.
Look at the color of the squash fruit and the condition of the vine. Squash fruit should be tan, brown or orange-brown depending on the variety, and the vine at the point of connection to the fruit should look like it’s dying.
In early winter, another way is to let the vine die from a light freeze and cut the vine from the squash fruit. A common method talked about is to press a thumbnail into the skin. When mature, the skin should be difficult to scratch or puncture. This is a rather subjective method, and I don’t like it much.
I don’t particularly like this method because it can puncture the outer skin. This puncture or wound is a possible entry point for rotting microorganisms if squash fruits are stored for any length of time. All fruits and vegetables should be handled carefully without creating damage.
Don’t pull squash fruits from the vine, because the wound left when the vine separates from the fruit damages the outer skin and leaves an open wound unless you’re going to cook or process it right away.
Cut the vine from the squash fruit, leaving about 1/2 inch of vine attached. They store better at garage temperatures than house temperatures.
Q: I had an African sumac tree removed. I believe that the removal crew treated the stump with something to prevent the tree from regrowing. Now the xylosmas I planted in that spot have yellow or brown leaves. Is flushing the soil with water the best treatment?
A: A common treatment to use on the stumps to prevent regrowth is applying potassium nitrate, aka saltpeter, one of the so-called stump removers. There is nothing poisonous to plants about the potassium or the nitrate. It’s the concentration of this chemical that does the job. It’s a salt.
Any salt applied in high concentrations will kill plants. It is not a good idea to apply table salt, because this salt contains sodium and chloride, both poisonous to plants.
But potassium nitrate is also a fertilizer. The dose makes the poison. This fertilizer is applied at a concentrated rate that kills.
As with all salts, they flush easily from the soil if you run lots of water through it.
There are other chemicals besides salt used to control regrowth from stumps. These are specific weed killers or herbicides that are very good at killing woody plants. Hopefully, these chemicals were not used.
The pictures you sent to me looks like some form of chemical damage. Hopefully, they used potassium nitrate, and you can simply flush the soil with water several times. If herbicides were used, the soil might need to be replaced in that area.
Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.