Pruning Flowering Shrubs at the Correct Time

Q. When is the right time to trim back the Desert Princess flower and Purple Sage bushes and also how far down?

A. I don't know a plant called the Desert Princess flower. If you can send me a picture maybe I will know it. I also do not know a plant with the common name of Purple Sage. I'm wondering if this is Texas Sage or Texas Ranger which is not a true Sage.

Texas Ranger in Bloom. Prune this plant after it finishes blooming this fall

            The general rule for pruning flowering woody plants is to cut them back after they finish flowering. So if a plant normally flowers during the summer and fall months then we would prune it back in the winter. If a plant normally flowers in the early spring, then we cut it back in late spring or early summer when it has finished flowering.

When plants like Texas Ranger get woody or leggy, remove one or two of the largest stems from the base. This is called gradual rejuvenation pruning.

            If these are small flowering woody plants then we could cut them back to within a couple of inches of the soil. If these are larger woody plants then we remove the oldest or most woody stems deep inside the canopy.

When pruning in this way, it is customary to remove no more than about one third of the total plant in a single pruning. If the shrub is still unsightly or overgrown, the following year we again remove one third of the shrub. In this way the shrub is in a constant state of renewal with new growth coming from the bottom and older, larger growth being selectively removed.

Rose Leaves Turning a Bright Yellow and Wimpy

Q. My vining roses have bright yellow and wimpy leaves. Am I over watering? Under watering? I have fertilized, added sulfur and iron too. 

Readers rose vine

A. This subject of whether a plant is over watered or underwatered is difficult to answer remotely. From your description, it sounds possible you are overwatering but probably not under watering.

Why don’t I think you are under watering? If you are under watering I would expect to see more leaf scorch and dieback on the leaves. Yellowing of the leaves of any kind is called “chlorosis” and can come from a number of sources including overwatering.

When yellowing or chlorosis is due to a lack of available iron then we will call it iron chlorosis. Chlorosis or yellowing due to a lack of available iron usually makes the leaves yellow with green veins. When iron is severely lacking, the leaf may be entirely yellow and scorched, but these are extreme cases.

Typical iron chlorosis with green veins on peach

Surround your roses with wood mulch, not rock mulch. If these plants have rock mulch surrounding them, rake it back a couple of feet and apply a couple of inches of compost first followed by some wood mulch. In this particular case do not use decorative bark mulch until the plants begin to recover. Decorative bark looks nice but it doesn’t do much for the soil.

Apply an iron fertilizer in the form of an iron chelate before you cover the soil with mulch. The chelate should be in the form of EDDHA which should be listed in the ingredients. The type of iron you add is very important. Mix the iron chelate in a bucket of water and pour it all over the soil above the roots or sprinkle it on dry and water it in. Don’t leave it on the surface because it is sensitive to sunlight.

Iron chelate with EDDHA on the label

Also, fertilize with a rose fertilizer or a fertilizer that has been formulated for flowering trees or shrubs. Avoid watering daily and try to give your woody plants a couple of days rest from any additional water before you irrigate again. Having wood mulch on the surface will help.

Specialty fertilizer formulated for roses

Always keep wood mulch a few inches away from the trunk of any plant to prevent stem diseases such as collar rot from occurring.

Older Star Jasmine No Longer Blooms

Q. We have a gorgeous, shiny dark green star jasmine, over 25 years old. About 5 years ago, it stopped blooming and nothing we've done has helped. Please help.

A. When that happens to older plants of mine I usually cut it back pretty hard and try to get it to regrow again, getting rid of some of the older wood.

Star Jasmine no longer flowering

Sometimes by cutting up plant back it restores some juvenility and it responds by growing more vigorously and flowering. I would also give it a good shot of fertilizer if you haven't already and soak the roots with a hose a few times, a few days apart.

Star Jasmine

It is late in the year to be pushing new growth so you could try this in early spring instead of now. However, star Jasmine is pretty hardy in our area so fertilizing it now should not affect its cold hardiness. It will respond with a flush of new growth next spring without any applied fertilizer.

This is a technique of applying a fertilizer late in the fall to get a spring response is called late fall fertilization. Fertilizer is applied in November before the leaves drop. Nutrients are stored in plants if they are not used up. If you combine late fall fertilization and cutting it back, cut it back first and then fertilize, not the reverse. Otherwise you would be cutting off parts of the plant that has stored nutrients. Let me know if this works for you.

Plant Onion Seed Now

Q. I would like to grow both yellow and red onions. When is the best time to plant them?

A. Onions for bulbs or green onions can be planted from seed mid-September through November in our latitude and elevation. Onions produced from sets or transplants should be started in March. They can be grown in a garden spot or 5 gallon containers. Onion sets, which are small onion bulbs, are

Contessa onion

easier to plant than transplants and usually have a higher success rate for most home gardeners.

Let’s focus on fall planting using onion seed. Growing onion from seed to produce green onions or transplants does not require very much space. Seeds can be spaced close together so I broadcast the seed, or sprinkle them, in the area where I want them to grow. The seed can be as close as ½ inch apart and even closer for green or bunching onions or even transplants.

For green onions just about any onion will do so shop for inexpensive seed. If you are growing transplants from seed then be more careful in your selection. I prefer sweet or specialty onions for transplants that I am growing into bulbs.

Big Daddy Onion

Las Vegas is in a transition zone so we can grow short day, long day and intermediate day varieties. These include the northern varieties like Walla Walla or southern varieties such as Vidalia. They just mature at different times. Varieties such as Candy, Big Daddy, Vidalia, Walla Walla, Yellow Granex, Bermuda, Texas Super Sweet, Contessa, Sterling, Red Marble and specialty onions like Cipollini, and Red Longa always do well in our climate and latitude.

Red candy apple Onion

Before planting the seed prepare the soil to a depth of 12 inches. Sandy soils that drain well are the best. We are not yet focusing on growing the bulb so any high nitrogen fertilizer will work well. You won’t need to fertilize them until after the seed is germinated. When you’re done mixing all the compost into the soil, make sure the soil is not “fluffy” so pack, roll or compress the soil lightly to make a firm seed bed.

Onions for transplanting, green onions or bunching onions grow well in containers or in blocks. They do not need to be planted in rows at this time. Carefully scatter the seed on top of the soil and cover the seed with about ¼ inch of topdressing or lightly rake the seed into the soil and add a light surface mulch.

Red Tropea Longa

Water the top dressed are mulched area twice a day until you see germination. Fertilize them after you see them begin to emerge. You can lightly broadcast a high nitrogen fertilizer on top of the mulch or topdressing and water it in. When you see germination reduce your watering to once a day. If onions are too close together, harvest and use some of them in a salad or stirfry to give them some space. As temperatures cool down and the plants get larger you will be able to water every other day and even every third day as it enters the winter. You will get larger transplants if you fertilize a second time with a nitrogen fertilizer about one month after the first one. Leave them in the soil all winter long. Dig up transplants in March or continue to use them as green onions.