Ask the Garden Guru

Yellow lower leaves in houseplants

Dear Garden Guru,

About once every week the leaves at the bottom of my houseplants turn yellow. Why does that happen? I would love for it to grow and have leaves on the stalk.

Anna in Berkeley

Hi Anna,

When lower leaves turn yellow and drop off, it is usually caused by under watering (the plant is kept too dry) or lack of fertilizer. It could also be a combination of the two. Another factor, though less common, is lack of humidity. When you water your houseplant, be sure to add enough water so that all the soil is moistened and the planter drains. It may be that you have to do this in the sink or tub if you are concerned with water harming the floor or furniture. I normally would not advise feeding houseplants in the winter months but you will do no harm if you were to feed with a half strength solution of Maxsea All Purpose once a month through February. This may arrest that lower leaf fall. The lower leaves (older) turn yellow because the plant is pulling all the nutrients and energy out to disperse to the upper (younger) leaves.

Keeping palm trees healthy

Dear Garden Guru,

What are tips for keeping palm trees healthy indoors?

A gardener in San Francisco

Hi A gardener,

Here are some basics for growing palms indoors.

1. Palms like bright, indirect light, or morning sun a few feet away from a window. Too much sunlight can burn the foliage, while too little light can cause foliage to stretch, become stressed or encourage bugs such as mealy bug or scale. Some palms can take more or less light than others.

2. Ample humidity is essential; palms are accustomed to high humidity, so daily misting of room temperature water with a spray bottle will help. If the room is dry (from air conditioners or heaters), leaves may shrivel and turn brown at the tips. Maintain humidity by allowing the plant to sit in a saucer filled with gravel/stones and water. Also, group plants together.

3. Feel the soil about 1/2” below the soil surface. If it is dry then it’s time to water, if wet then leave alone for a few days. Never leave the plant sitting in water — it can lead to root rot.

4. Air flow is also important, without proper air circulation, your plant may be at risk for spider mites.

Indoor grass & cactus garden

Dear Garden Guru,

I have often seen indoor grass and cactus gardens. These are often planted in shallow rectangular pans. What is your recommendation as to the types of grasses to plant in these pans for display in a coffee table or windowsill?

Jaime in San Francisco

Hi Jaime,

The easiest is oat grass (cat grass). This is sold as seed from our Botanical Interest line. The second best would be using the Pacific Park Blend Fescue seed but the smallest amount is 1 pound.

Sunrise Cactus

Dear Garden Guru,

I have a Sunrise cactus which is very similar to a Christmas cactus. It had beautiful blooms when I bought it but I cannot seem to get it to bloom again. Any suggestions?

Christine in Daly City

Hi Christine,

The Sunrise cactus requires short days and cool/cold nights to initiate bud
formation (Classic October/November weather). Your plants would do best
outdoors now until frost, in a partial shade location. Also, let the plants
dry out between waterings.

Rot at bottom of cactus

Dear Garden Guru,

Can you help me with some rot that is eating away at the base of a large columnar cactus a friend just gave me? The plant looks healthy overall, but at the base a good chunk has rotted away. Any help to save it would be appreciated! Thanks.

Michael in Oakland

Hi Michael,

Rot at the bottom of a cactus is not good. It is usually caused by cold, wet soil in constant contact with the base of the plant. This is the reason you see a 1/2 inch or more of gravel in potted cactus and succulents. The only thing you can do now is to cut out the rotted part. It would be easiest to unpot the cactus for the operation. Using a clean, sharp knife, you will want to cut away around the rotted area in the healthy tissue. Disinfect the wound with a 5:1 water bleach solution. Allow the wound to dry and callous for about 2 weeks before repotting. Do not let the calloused wound have contact with the soil.
Another option would be to cut off the cactus from the rotted bottom. Allow the cut cactus to dry out for 2 or 3 weeks before repotting. It will begin to make new roots in about a month. In this situation, frequent watering is desirable. Good luck.

Plants for an office cubicle

Dear Garden Guru,

I wanted to get some plants for my husbands cubicle at work. What are the best indoor plants for a desk that doesn't get any natural light? Mahalo.

Marlene in San Francisco

Hi Marlene,

Foliage plants will last longer than floral items. In 4″ or 6″ pots you can find Pothos, Dracaena marginata, Nephytis and Spathiphyllum. These have relatively no problems with insects or fungus and will be happy with fluorescent lighting. Should you want some color, Bromeliads are long lasting choices.

Cracks on jade plant

Dear Garden Guru,

I bought a Jade plant about 2 months ago and had originally placed it in the window sill where it would receive alot of direct sunlight. However the stem of the plant seemed to have almost "cracked and developed brown lines running throughout them. The leaves look fine. I then moved the plant to a spot that gets a lot of indirect/ filtered light hoping this would repair or heal the plant. However i have had no luck. Any thoughts?

Maria in San Francisco

Hi Maria,

I think that the cracking you describe may be a symptom of over watering. Jade plants, like other succulents will accumulate excess water as they depend on these water stores during long dry spells. Your Jade does not know that it is going to be supplied with endless irrigation and has literally busted its gut. I would withhold the water for awhile, maybe just water every other week.

Removing moss growing in containers

Dear Garden Guru,

What can I do about the "moss" that grows in the soil of the pots I keep on my deck, containing herbs and flowers? I saw a product to kill moss in grass, but I don't know if that is appropriate here. The "moss" starts as a single sprout of fine leaves coming from a center, quickly multiplies into a thick growth and then send up little shoots with a yellowish top, like a flower bud.

Ellen in San Francisco

Hi Ellen,

Moss usually grows in cooler, moist locations. The best way to keep the moss from spreading is to remove it before the “flower buds” ripen to rust brown. These structures are in fact spore producing bodies called seta. The whole clump can probably be peeled off the soil. You can then remove the top 1/2 inch of soil with a small trowel in the attempt to rid the soil of any dormant spores. Adding the lawn moss killers to your containers is not a good idea. It is possible you may get the same effect applying EB Stone FST or Liquininox Iron and Zinc to the containers. The moss, by the way is not really that detrimental to your plantings.

Pruning a jade plant

Dear Garden Guru,

How do I prune a Jade plant, 2 1/2 feet tall, potted, that is getting lanky? What about its flower? I would like to broaden its stems and have it grow fuller. Thanks.

Sfenerty in Inverness

Hi Sfenerty,

The Jade plant can be pruned by cutting just above an old leaf scar, seen as a faint line around the stem. New shoots (a pair) and leaves will sprout at this scar. The pruning will “broaden” your stems twofold. Flowering for the Jade plant begins in late November usually. They require full sun to do so reliably.

Reblooming aloe plants

Dear Garden Guru,

I have an aloe plant that is about 3 - 4 years old. I believe the plant is getting ready to bloom. It has many baby plants growing on the base. Should I remove the little babies? Should I expect the plant to bloom every year? How many blooms should I expect? How long does it take to bloom? Thank you!

Isis in San Francisco

Hi Isis,

You do not need to remove the babies unless you want to start more Aloe clumps. Eventually, all the plantlets will bloom along with the parent giving you that much more of a show. You can now expect that the “mother plant” will flower each year. The Aloe flower stalk will elongate 1′ to 2′ above the plant. There are usually 6 to 12 flower buds on each stalk that last about a month.