Shrubs not growing

Brisbane, CA(Zone 10b)

I have a few shrubs that I planted last fall have grown VERY little. However, they are not dead. I added compost, fertilized them with Osmocote and lately VF-11. Some of them are supposed to be fast growing shrubs like Sumac Grow-Low and Moonlight Scotch Broom. These two were planted on the same steep hill but others were in different places but all on slopes. I did notice when I water them by hand, water just run down the hill. It doesn't look like the soil is absorbing the water very well. They do get water from drip irrigation though and the leaves are green. The soil test indicates low nitrogen and high phosphorus. Could this be the reason? I also wonder if the soil around them is too hard that I didn't dig the hole big enough to give them better soil.
Thank you in advance for your advice.

Ayrshire Scotland, United Kingdom

I think you have answered your own question, where ever you want shrubs / tree's to grow well, you need to prepare the soil well before hand, (They have to be in the same soil for many years unlike some flowers) add as much humus as you can to the planting area, when you dig a whole for tree's / shrubs, you need to dig 2 times as deep and as wide, then add all the humus (horse manure well rotted, no smell tells you it's usable) add a few handful's of fish / blood / bonemeal to the soil you put back into the hole as that is a slow release feed and organic too.
Because you've planted on a slope, what you need to do is make a horse show wedge in front of the shrubs (lowest part of the soil, this way when you water, there will be some caught in the wedge and this may help the water drop down into the root area.
Or the best way is dig a hole at the root area, take a clear plastic juice container with the bottom cut off and the cap removed, place the container into the hole, cap end down, and back fill with soil, when you water, you fill the container up with water a couple of times and this goes right down to the roots, BY the way, a Drip water set up will never be enough water addition to give a good watering, shrubs / trees need a good soaking every couple of days for the first couple of years till they get established, the clear container is a good way to add a liquid feed when needed too.

Hope this helps you out a bit and good luck.
Best regards. WeeNel.

Brisbane, CA(Zone 10b)

Thank you WeeNel. I think you are right, especially about the watering part. At first I thought I didn't dig the hole big enough, so I made the hole bigger and added whole bunch more compost. Didn't see much change. I was surprised that with so much humus soil, water still does not seep in very well. Probably due to the steep slope of our property. Come to think of it, the most growth I have seen in them was right after our raining winter season. I also purposely did not water some of them very much during summer as they are planted near our 2 native live oaks. I understand it's important to keep area near them dry during summer. Just bought some watering spikes. I have a feeling that this will improve the situation. Thank you again for your advice.

Contra Costa County, CA(Zone 9b)

Build up a berm around the downhill half of the planting hole so when you water it does not run off.
Some drip systems apply the water fairly fast, so this can help, even now.
Some drip systems apply the water REALLY SLOWLY so you need to run them for many hours.

If the soil test shows low nitrogen, then this is a prime reason for slow growth.

Fertilize right now. As the weather cools but the soil is still warm from the summer the plant roots are highly active, and will take in the fertilizer very quickly.
Fertilize again in January. Let the winter rains water it in, or else you water it in. Then the fertilizer is in the root zone when the plants start growing again in the spring.

Being in zone 10 is great: no frost for several more months (if any at all) so your plants can grow some before they go dormant. Then they may be dormant for only a very short time before they are ready to grow again. Where I am (zone 9b) I apply fertilizer at the end of January and into February for spring growth. And many plants are growing then, too. Unless we get a late freeze, 'Spring' is here by February, even if the calendar says 'Winter'.

Yes, protect the oak by minimizing the water under it. Oaks are accustomed to water in the winter, so if it does not rain, it is OK to water your shrubs then. They won't need much, but a deep soaking about once a month Nov, Dec, Jan & Feb would not hurt the oak, and would help the shrubs. I would water them a bit deeper, but not very often next summer. Maybe every 2 weeks if they can go that long between watering. The summer after that they will probably go even longer between watering. Maybe a deep soaking once a month.

(Zone 7a)

Also, plants take awhile to adapt to the new site. Your plants could just be laying down new roots at the expense of branching and foliage. I've had plants take up to 3 years before really taking off.

Brisbane, CA(Zone 10b)

Thank you, Diana. I got some blood meal to add around my garden to increase nitrogen but not phosphorus. All my soil tests show low N and high P, regardless it's soil in the ground or planting mix bought from nursery. I thought it kind of strange because I read the P is usually low in natural soil and high in planting mix (from manure).

Kwanjin, you raised a good point that I was also wondering about. Does the size of the shrub makes a difference in how fast the grow? I bought these shrubs from online nurseries for wider varieties to choose from. However, to save on shipping, I chose smaller sizes. Maybe I should have just paid more and got the largest size. But I also read bigger shrub get affected more by transplant shock.

Ayrshire Scotland, United Kingdom

Most plants have some shock affect them when transplanted BUT the larger the plant, the bigger the expectation of transplant shock. these larger plants have more foliage, more shoots / branches, larger root areas so naturally there is a larger problem for the shrubs / plants / tree's to have to cope with.

There has been studies done about this very subject re transplant shock.
A bed was planted with smaller shrubs, another side by side, same soil and treatment was planted with large shrubs, it was amazing.

The smaller shrubs took a few weeks to perk up again and even lacked new growth for many months. BUT they did pick up and begin to grow well the following year and continued there after.

The larger shrubs lost MOST of there foliage, some of the tender side tips of the shoots turned brown and required pruning, some looked like they had died off, However, they did perk up a bit, they took a lot longer to resettle into the new environment and they never really looked happy or growing for a couple of years although, they did regrow foliage when in recovery.

The end result was the smaller shrubs grew faster, stronger / more healthy looking far quicker than the larger shrubs BUT after about 3-5 years, the smaller shrubs grew much faster and were catching up on the taller shrubs, so at the end of the day, the story is, if you want to wait for a plant to mature and pay less, go for the smaller type, IF you want instant planting but more worry about the shrubs making it through the transplant , the regrowth, then the gambling when the larger type plants take even longer to show signs of recovery.
Personally I think it all depends on the proper care given, the watering, the soil conditions, the sun / rainfall and the prep when readying the area for new shrubs, this must have a influence also and will play a huge part in good recovery, so my personal view is, be patient and go for smaller shrubs that suit your pocket money more than a huge plant you have spent a fortune on but along with that is the huge worry watching you money turn brown and maybe dying.
There's an old saying. "small parcels make for large impact"
Best Regards. WeeNel.

Contra Costa County, CA(Zone 9b)

Ditto the research posted by WeeNel:

1 gallon and 5 gallon shrubs, same species, same conditions.
The 1 gallons grew quickly, the 5 gallons more slowly.
The 1 gallons caught up to the 5 gallons in just a couple of years, then continued growing faster, and overtook the 5 gallon plants.
This was a really old study. I heard about it in college (mumble... mumble) years ago.

Brisbane, CA(Zone 10b)

Very interesting study indeed. I gotta tell my husband about this. He sort of hinting a couple of times that I should have paid more for bigger plants. I now try to buy new plants from local nurseries so that I can get bigger ones w/o paying shipping charge. Our garden is just one year old. We both eagerly want to see results. Gardening certainly teaches us patience, among many other good virtues. Thank you both.

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