Ask the Garden Guru

Growing sweet peas

Dear Garden Guru,

When is the best time to plant Sweet Pea starts? When are they for sale? Thanks!

Lisa in Novato

Hi Lisa,

Alas, the best time to start sweet peas in your climate is in October. Planted in the fall, they develop strong root systems and then take off in the spring. Both seeds and starts are available. The second best time is in February. Our stores will have packs of tall-growing sweet peas available in a variety of colors.

Rose Pruning

Dear Garden Guru,

I'm pruning my roses. Some are very tall. Is it true that if a branch of a rose bush has no thorns, it is a sucker? I've tried to get down to the bottom of the bush to see if the branch is coming from the base of the bush or from the ground. I can't always identify so I was wondering if the absence of thorns makes a difference. Any help would be appreciated. THANKS!!

Lorraine in Walnut Creek

Hi Lorraine,

Unfortunately, the lack of thorns does not indicate whether you have a sucker or a cane.  Many rose bushes will throw almost thornless canes occasionally that produce an umbel of flowers. They are difficult to prune in that they don’t always have a well oriented leaf bud scar to make a cut above.  You really do have to see if the origin is coming from beneath the bud union or the root zone. These thornless canes are often skinnier than there thorny sisters which makes it even harder to tell.  You won’t be hurting anything if you feel you must remove it just to be sure.

How to make Wisteria bloom

Dear Garden Guru,

I have a wisteria vine. It barely blooms and produces just leaves. I want to thin it out to bloom. Will that help?

Larry in Rio Vista

Hi Larry,

Dear Larry,

If you’re pruning your Wisteria each fall or winter, you may be pruning off the flowering wood. Wisteria only blooms on old wood. It is recommended that only the long, looping tendrils be cut back. Flower buds can be seen as largish, oyster shell or triangular shaped “scales” on the older wood behind these newer growths.

Another reason for a lack of bloom is over-feeding. Your Wisteria can get by without any feeding at all. Really! Your thought about opening the vine up with the chance of providing more sun can be done, but again, you may be removing flowering wood without knowing it, and pruning out the older wood will result in a large flush of new growth in the spring.

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.

Something eating my Abutilon!

Dear Garden Guru,

My abutilon has some sort of pest. The leaves have several holes (all over the place not concentrated in center or edges). Most of the leaves are affected. I have an abutilon right next to the one with the problem and it is unaffected (though a slightly different variety of abutilon). Thoughts on what to do?

David in San Francisco

Hi David,

Sounds like Slug or Snail damage. The best way to be sure is to check at nighttime, as most leaf eating pests are nocturnal. Slugs tend to like moist shady spots, which we assume is where your Abutilon is located.

The solution is to try picking off and discarding any you see, and using Sluggo snail and slug control to eliminate the ones that come out of hiding. This is a non-toxic product that is safe to use around pets. Slugs usually die within 4 to 6 days after eating it. Sluggo lasts about 3 to 4 weeks and then breaks down as an Iron fertilizer. Reapply as needed.


Dear Garden Guru,

I have had a Brugmansia Charles Grimaldi for at least 7 years and have had numerous problems with it such as aphids, snails. etc. I have told myself that I am not giving up on the plant, but it has never flowered. Is there such a thing as a male and female tree and do you think that I am missing one of those? Help!

Julie in San Francisco

Hi Julie,

Brugmansia are very much dependent on daylight to trigger blooming. They will start to set buds when  the days start becoming shorter and nights become cooler, usually late August to September.  Also Brumansia stalks must become forked before they produce flowers. Growth below the fork is juvenile or vegetative.  Growth above the fork is considered adult or flowering.  Have you cut the plant back so that there is no fork?  Are all the stems and trunks on the plant still straight?  The plant does not require male and female.

Feeding azaleas, camellias and hydrangeas

Dear Garden Guru,

Dear Garden Guru, I feed many acid plants [azalea, camellia, and hydrangeas]. Is the same acid-based food good for magnolias and hibiscus?

James in San Francisco

Hi James,

Thanks for your question. With regards to Magnolias, they generally like neutral or SLIGHTLY acidic soil. So, yes, you can use your acid food for them, but you may want to dilute it a bit from regular doses, and don’t use it as often as the instructions say for true acid-loving plants.

As for Hibiscus, I’ve referenced some instructions from the following website, as they are excellent.

“Hibiscus produce their most and best flowers with a fertilizer high in potassium – that is the third or last number in the formulas often given on fertilizer containers. Sometimes, people are tempted to use the “super bloom” type formulas which are very high in phosphorus – the middle number of the formula. This is NOT GOOD for hibiscus as research has shown that high phosphorus can prevent hibiscus from absorbing other nutrients it needs. These types of fertilizers may be sprayed on the leaves of the plant as a “foliar feeding” but should not be added to the pot.

If you use a local brand, it’s good to check that the plant food is complete – that it contains “minors” which are small amounts of minerals that hibiscus also need. They will be listed on the side of the container. Look for ingredients like copper and iron. Be sure to follow the directions that come with the package of fertilizer. Hibiscus like to be fed small amounts often rather than large amounts occasionally. If you can hook up your water hose to a proportioner or fertilizer injector, you can water and feed easily at the same time. Otherwise mix your water and water soluble plant food in a container and pour enough of the solution into each pot so that some comes out the bottom of the pot. Fertilize when the pots are moist, not when they are dry. Use plenty of plant food in the summer and less during the winter.”

At your local Sloat Garden Center, you will find that we carry a Hibiscus specific food that does meet these suggested requirements. And that is what I would recommend for success with growing yours.

Anigozanthos Care

Dear Garden Guru,

I've purchased several anigozanthos (Kangaroo Paw) and after a beautiful bloom this summer, they've all turned brown, dry and look dead. Is this normal? Do I merely cut them back and wait for Spring? Last year I threw all of them away as I thought they were dead, but maybe I've been mistaken. Please advise. Thank you.

Karen in San Francisco

Hi Karen,

Thanks very much for your question. It is normal for the flowering stalks of Anigozanthos to turn brown and dry up towards the end of summer. The leaves, however, should still be green. If the whole plant has turned brown, it may be that it was over watered or in soil that did not drain well or that it was too dry. They also do not like fertilizer with Phosphorous. Here is a check list to keep the plants alive:

  1. Plant in a sunny location. If you live where there is frost, plant under the eave of a house or high tree canopy
  2. Give excellent drainage (lots of compost or sand/gravel)
  3. Where it is dry in the summer, they need regular water
  4. Do not feed heavily and avoid Phosphorous (middle number)
  5. After the flowers have died, remove the stalks and leaves to almost ground level. Each “fan” of leaves only flowers once. Be careful not to cut or damage new fans that are forming. These will flower next year.

I hope this helps. As always feel free to visit any of our stores for more expert advice!

Rose Transplanting

Dear Garden Guru,

We would like to transplant our roses. They are in an area that does not appear to be the best and the leaves are being eaten by something. When is the safest time to move them and what do we need to do to make sure the move is a successful one? Thanks for your help.

Shauna in Pacifica

Hi Shauna,

If you can wait, the best time to transplant your roses is late November or early December. This is the time that they begin their dormancy. You can do all your pruning before you move them and treat them like a bareroot, meaning you won’t have to get the entire rootball. It is best to have the holes already prepared, usually about 1′ deep and 2′ wide. You will want to amend your soil with organic matter such as EB Stone Rose Mix. Additional Alfalfa meal and or bone meal at the bottom of the hole will help the plants “bounce back” rapidly when the weather begins to warm again in February.

As for holes in the leaves, as a general rule, if the middle of the leaves are being eaten it is slugs or snails. If the outer edges of the leaves are being chewed, it is caterpillars.  At all of our Sloat locations near you (San Bruno – 675 El Camino Real; 2700 Sloat Blvd, San Francisco) we have products to help fight these insects/bugs. Of course, you can also try plucking them off your plants early in the evening or a bit later with a flashlight too!

I hope this helps steer you in the right direction.  And as always, visit our stores for more expert guidance.

Moving a lilac tree

Dear Garden Guru,

We have a large lilac already in our back yard, but we are re-designing the garden in a modern/asian style. I would like to move the tree from the center of the garden to a place across the yard that is by the steps and therefore not the first thing you see. It will still get about the same light. Will it die if I try and move it? What steps can I take to ensure it's health and how do I dig out all the roots? Thank you!

Stephanie in San Francisco

Hi Stephanie,

You would be best waiting until late fall to transplant. Follow the steps below.

  1. Ensure that the plant has been watered in the previous 72 hours.
  2. The top growth of the plant should be pruned back at least 25% to lessen the stress on the soon-to-be damaged root mass.
  3. Have the new hole dug and prepared with organic material and some agricultural lime.
  4. Begin to dig around the plant (24-36″ away form the trunk) with the goal of creating a root ball 18-24″ across and 24-30″ deep.
  5. You will need two people with shovels to gently work the root ball loose and surround it with an old sheet or burlap tote.
  6. Once wrapped, the plant can be moved to the new hole and planted at the same depth, adding Sloat Forest Mulch Plus, Agricultural Lime and Sure Start fertilizer
  7. Water heavily and wait. All remaining leaves may drop off but that is OK as long as the branches and stems remain firm and don’t turn black.
  8. Come spring you should see a surge of growth. Don’t be surprised if the plant does not bloom that first year after transplanting.

Curious if we have your favorite plant or product in stock? Call one of our locations directly and we'll be happy to check.