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Getting rid of powdery mildew

Dear Garden Guru,

My neighbor gave me two beautiful rose trees in large pots. The stems/flowers have white powdery mildew on them. How to I get rid of it?

Nancy in Danville

Hi Nancy,

You can treat the powdery mildew with Monterey Bi-Carb. This is an old-fashioned but effective wettable powder (potassium bicarbonate) that kills the mildew on contact. It is safe for use in organic gardens. Another remedy is using Serenade spray. However, to prevent mildew in the future, you can spray roses with Neem or horticultural oil. The powdery mildew spores cannot penetrate the leaf through the oil film.

Lemons with thick rind

Dear Garden Guru,

For several years, my lemons have had a thick rind and little juice in them. I put a Meyer lemon tree in about 20ft away and it's starting to put out lemons this year. The rind again appears a bit thick. What's missing in my soil? I am using a citrus and avocado fertilizer. AG

AG in San Francisco

Hi AG,

There are two reasons that the rinds of citrus become thick and both are nutritional. The first is overfeeding with a food high in nitrogen.  It is recommended that a basic citrus fertilizer be fed in spring and again in fall along with a supplement that contains zinc such as FST.  The second reason is a deficiency in phosphorus ( the more likely cause).  To avoid providing an excess of nitrogen, you can supplement the recommended feedings with 0-10-10.

Help with dry lemons

Dear Garden Guru,

Why would lemons be dry and not juicy. It is sunlight?

Linda in San Francisco

Hi Linda,

There are a few environmental factors that will cause lemons to be dry. One is water stress. If the trees were not irrigated enough during the growing season, the tree will pull moisture out of developing fruits in order to keep the leaves healthy. Another is cold damage. When ripe or ripening lemons are exposed to freezing or frosty conditions, the moisture in the fruit dissipates. The most common reason for dry fruit is that the ripe lemons are left on the tree too long. Hope that helps!

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.

Which fruit trees in the Richmond district?

Dear Garden Guru,

We are moving to the foggy Richmond District and would like to plant a fruit tree or two along the edge of our yard. What grows well in that area, and when should we plant? Thank you!

Lauren in SF

Hi Lauren,

You would do well with an Apple, such as Fuji or an Asian Pear (20th Century variety is self- fertile). You could also grow a European pear, but they do best in pairs (no pun intended). Lemons would also fare well. The best time to plant deciduous fruit trees is in January or February. You can plant citrus nearly year round.

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.

Mediterranean, bee-friendly fruit, vegetable and flower recommendations

Dear Garden Guru,

Can you recommend a list of Mediterranean climate tolerant herbs, fruits, veggies, and flowers which attract bees and humming birds? Any guidance will be much appreciated.

Wayne in San Francisco

Hi Wayne,

First tip is to take care of the soil. Don’t skip on the amendments that will help retain moisture and offer nutrition. Water regularly, especially the flowers and vegetables. Choose organic fertilizers that will not harm the beneficial soil organisms that help your plants’ root systems by improving nutrient uptake and guarding against disease. Actinovate is a wonderful supplement for any new garden plant.

Vegetables: peas, lettuces, chard, beets, cabbages, broccoli, mustard, spinach, carrots, radishes, kohlrabi, arugula (actually all your greens), in the summer- cherry tomatoes too. Herbs- parsley, cilantro, rosemary, chervil, savory, sage, thyme, oregano, marjoram

Fruits- raspberries, southern highbush blueberries, apples, pears, strawberries, loquat, pineapple guava, lemon, kumquat, Trovita orange

Flowers that attract beneficials and pollinators- white alyssum, cosmos, achillea, agastache, tulbaghia, Oenothera, Eriogonum (Buckwheat), Erigeron, Dianthus

Hummingbirds- Abutilon, Fuchsia, Agastache, Salvia greggii, Salvia clevelandii, Nasturtium, Delphinium

There is so much more, but this will get you started.

Lemon tree pruning questions

Dear Garden Guru,

We recently moved and inherited a lemon tree that hasn't been pruned for maybe a few years. While some branches still have small, thin-pith lemons, others have reverted to grapefuit-sized thick-pith giants and the whole tree is sprouting lots of growth. When should I hack it back and how much can I prune off at one time? Do I have to wait until it’s dormant? It still has lots and lots of lemons. Thanks!

Paula in San Francisco

Hi Paula,

You can prune your lemon at any time of year to shape it. There will always be a point where some lemons will have to be sacrificed. Pruning in the fall after most of the fruit is ripened will preserve the most fruit. The larger pithy fruits are likely over-ripe and have been on the tree too long, so they should be removed. You can prune the tree as hard as you want but avoid exposing the trunk and limbs too much to avoid sunburn. Remove any growth that has thorns (juvenile foliage) or growth that is coming from below the graft (seen as a thick “collar” towards the base of the tree).

Saving water for outdoor plants

Dear Garden Guru,

I am saving the rinse water from the washing machine to water the potted plants. What effect will that have on the outdoor potted plants?

John in Bay Area

Hi John,

Dear John,

The rinse water from the washer is fine for potted plants as long as you are using a biodegradable detergent. Liquid detergents are better than powders. Avoid any that contain chlorine bleach, boron/borax, and any ingredient with the word sodium in its name. Also, if your water is softened, it contains salt.

The one concern with greywater is that you can get a build up of harmful salts if you use it on the same plants or the same area repeatedly. We recommend saving and using the rinse water, versus the wash water, because it will contain more dilute amounts of soap.

Container flower recommendations

Dear Garden Guru,

We just moved from the east coast. What container flowers/plants do you recommend for a west facing deck?

Karen in SF

Hi Karen,

aeonium_arborescens_tip_top-jpgWelcome to the Bay Area and away from east coast winters. The only issue is what you can’t put into containers. There is a vast array of plants to choose from. My favorite go-to plants are succulents. I like to choose Aeoniums for height, echeverias, kalanchoe paddle plant and Crassula for a bushy shape and then sedums, sempervivum, senecio and ice plants to trail over.

For color, I like to go with lavenders, salvia, kangaroo paws, agastache and lotus or calibrachoa to trail over. These are drought tolerant as well. Use a large pot and soil moist granules for less watering. An added bonus is that most of the plants for color attract hummingbirds. You can even mix the succulents with colorful plants; all like the same light and have similar watering requirements. Hope this helps.