Eggplant fruit production slows down in cool weather

Q: Will my eggplant plant continue to produce through the fall and winter?

A: They are warm season vegetables, so they slow down considerably as temperatures drop.

Although eggplants will keep growing and flowering, they are more productive if cut back and allowed to regrow during late summer. Cut plants to about 6 to 8 inches in early August, cut at a crotch, fertilize and allow them to regrow.

Fertilize and keep soils moist to force them to regrow. The second crop will be ready to harvest in about six weeks after cutting them back. In Louisiana, eggplants are sometimes trellised and sheared late in the season for increased yield and quality.

The ideal temperatures for eggplant is 70 to 80 degrees Fahrenheit in the day and 65 to 70 at night. Very few places, outside of a greenhouse, give those types of temperatures consistently. Obviously, they do well in temperatures higher and lower than this. Fruit abortion can begin around 95 degrees even though the plant itself can handle heat.

As temperatures drop in the fall, eggplant still sets fruit, but fruit set is not as reliable and development is slower. Eggplant is generally more sensitive to cooler temperatures than its cousins, tomatoes and peppers.

Flowers consistently set fruit down to 60-degree nighttime temperatures. Eggplants begin to get chilling injury at temperatures below 50.

Staking may be necessary if plants get big and full of fruit. Fruit touching the ground will spoil.

Harvest fruit when they are one-third full size and shiny. Overmature fruit will be spongy, the seeds begin to harden and the fruit surface becomes dull rather than shiny.

Snap fruit off of the plant, but they will keep longer if they are cut from the spiny stem. Mulching helps fruit to set and improves fruit quality.

Q: I have two pink dwarf oleanders planted in 18-inch clay pots which are healthy looking but very few blossoms. One of my “expert” friends says simply that “oleanders don’t like pots.”

Another “expert” says that I’m watering too much. Are either of these guys right or do you have any suggestions that might get some blossoms?

A: We have dwarf oleanders at the research center in containers and they bloom just fine. The usual reasons for a lack of flowering are not enough light and pruning them incorrectly. Oleanders use a lot of water when it’s present.

There might be a couple of things you could try. Oleanders should be in full sun. They love the heat, and they love water and fertilizer to perform their best.

If the container is smaller you might have to water more often. Eighteen-inch containers are not that large and don’t contain a lot of soil. If the soil volume is not large, the plant may not have enough water in the soil to last between irrigations.

Oleanders that are not getting enough water will look normal but have a very open canopy and not bloom well. Containers are not very forgiving when it comes to water. The water in that soil can be used up fairly quickly.

You can try using a soil moisture meter that you can buy from the nursery for about $7 and check the soil moisture before you water. Water when the meter is about halfway between wet and dry; do not let the soil go totally dry.

Next, use a fertilizer like Miracle Gro or Peters and water it into the soil about once every six to eight weeks. Oleanders growing in the ground do not need to be fertilized as often.

Next, cover the soil in the container with mulch to help keep the soil moist. About 3 inches would be enough.

If oleanders are young or if they are pruned with a hedge shears they will not produce any flowers or very few. Don’t prune it with a hedge shears if you want flowers, contrary to how you see it done around town.

Q: I purchased dwarf oleanders two years ago in 5-gallon containers. They are doing fine but are about 4 feet high. It is my understanding the plants can be pruned. I need to know the best time to do so and how far down to go without harming them.

A: Pruning oleander is very simple, much simpler than many other plants. You can prune them any time of the year without any problems. Having said that, they are usually pruned during the winter, late winter or very early spring.

Use loppers, the pruning shears that have two handles and you have to use both hands. Count the number of main stems coming from the base of the plant. Identify the two or three that are the oldest. They will be the largest in diameter.

Remove these oldest ones within a couple of inches above the soil. You are done for this year. It takes about 10 minutes and no mess to clean up. If there are some unusually long ones remove them from the base as well.

Repeat this about two or three years later. Continue this cycle of removing the largest diameter every three years or so.

Please do not use any hedge shears unless you don’t like the flowers. Having said all this, the absolute best time to do this in Southern Nevada is February but you can do it any time without damaging the plant.

Q: Having had several somewhat expensive repairs because of root damage to my sprinkler system, I am wondering if you have any suggestions for preventing/lessening such damage. I was told by one sprinkler technician that putting copper (he suggested pennies) in the ground would discourage root growth in the area. Is there any truth to this?

A: I am guessing the root damage was lifting the pipe out of the ground because roots were growing under the pipes. Roots will not grow into pipes unless there is existing damage to them, allowing for their entry, but then there would be water everywhere. The other type of intrusive growth would be into drip irrigation emitters.

The best ways to avoid damage are to bury pipe deep, plant woody plants far enough from the irrigation pipe so that it does not become a problem (preferably outside the irrigated zone of the plant) and use the appropriate type of irrigation pipe.

Irrigation laterals (pipes coming from irrigation valves directly to a sprinkler or other type of emitter) should be a minimum of 12 inches deep. Irrigation lines that are under constant pressure (pipes before the valves) should be a minimum of 18 inches deep.

All plastic pipe used for irrigation should be a minimum of Class 200 PVC when installed after or downstream of the valve. All pipe under constant pressure (before the valves) should be Schedule 40 PVC.

Class and Schedule refer to the internal pressures that these pipes can withstand, which is related to the thickness of the walls of the pipe. All pipe installed should be “fresh” pipe, undamaged by the sun.

Do not use, or do not let a professional use, PVC pipe that is discolored. Pipe exposed to the sun should be painted or wrapped. Paint will protect PVC from the sun’s damaging ultraviolet radiation.

As far as pennies are concerned, this idea comes from the fact that copper is very toxic to plants. Copper sprays are used to control some fungal diseases. Copper is also used to control mildew, which is a plant; copper is used to control algae and mosses, which are plants; copper will kill plant roots when used as an appropriate pesticide (yes, it is considered a pesticide if it kills plant roots); and copper nails will kill trees if pounded into the trunk a few inches apart.

The copper that kills is called elemental copper and must be available to react with plant roots. Perhaps plant roots in direct contact with pennies will be killed but plant roots just a few inches away probably will not. This would mean that if you were to protect the pipe you would have to line the pipe with pennies.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at Send questions to

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