Trustworthy Garden Information

Oct 24, 2020

Trustworthy Garden Information

Oct 24, 2020

By Susanne von Rosenberg, UC Master Gardener of Napa County



These days you can get gardening information just about anywhere. In addition to the internet, there are radio shows, books, TV shows and classes offered by various organizations to help you learn. Even many gardening catalogs include educational tidbits.


But how do you know whether you can trust the information you're seeing? We all know to take information from an unknown source on the internet with a grain of salt. The easiest way to know whether information found online is reliable is to look at the source. If it's from a research organization, such as a university or state agricultural agency, the information will be reliable.


The same is true for information from Master Gardener programs. Master Gardeners provide science-based gardening information.


If you can't easily verify that your information source is reliable, try doing an internet search on the main points to see if a scientific source or paper supports them. This can be harder than it seems, because gardening advice online often simply repeats what someone else said, and the original source can be challenging to track down.


Books and other written materials often have references to document where the information came from. Verifying the accuracy of what you hear on the radio and TV is more difficult. You can check the education or experience of the presenters, but even if they have a background that would enable them to provide reliable information, there is no guarantee that they will.


Before acting on information that you're hearing or reading, make sure it's relevant to our climate. A lot of recommendations online about citrus care come from the University of Arizona. That state's climate is very different from ours, so although the information is scientifically sound and reliable, it's not relevant for Napa County. If you're wondering whether you can rely on a particular piece of advice you've found, you can always check with the Master Gardeners by email or phone. We can let you know if what you're considering is sound.


Some gardening myths are well established and have been around for ages. A recommendation may be very precise and sound scientific, but that doesn't mean it's correct. Here are three common myths.


“Put coarse material at the bottom of containers for improved drainage.” No one knows how this myth got started. It's true that plants need good drainage so that the roots can receive oxygen. It's also true that containers absolutely need a drainage hole.


What most people don't know is that it's hard for water to move from fine-grained soil (such as potting mix) to coarser material (such as gravel). The water has to saturate the fine-grained material first. So, by putting pebbles at the bottom of your pot, you're actually encouraging the problem (waterlogged soil) that you're trying to prevent. The best course is to fill the entire pot with high-quality planting mix. You can also elevate the pot slightly so that water can drain more easily.


“Use Epsom salts to fertilize your plants.” Epsom salts provide magnesium and sulfur. They are soluble, so they dissipate in soil that receives regular irrigation or rainfall. This may sound like a good thing, but what it really means is that the excess is likely to end up polluting groundwater.


Epsom salts possibly got their reputation as a fertilizer because they can help relieve magnesium deficiencies. One sign of magnesium or sulfur deficiency is chlorosis in leaves, which causes yellowing of the tissue between the veins. Chlorotic leaves are less productive and die sooner. If you can cure the deficiency, leaves will recover and overall plant health will improve.


But if your plants aren't magnesium-deficient, Epsom salts won't help them grow. Magnesium deficiencies are best solved with a slow-release source of magnesium. Most magnesium deficiencies occur in intensely cultivated soil, or in light, sandy soil. Before adding any chemical to your soil, make sure it's necessary and ask yourself whether it could do harm.


“We can rely on gardening wisdom from the past.” Gardening practices were arguably more sustainable in times past when synthetic fertilizers and pesticides didn't exist. Certainly, overreliance on these products has harmed soil health and the environment, and fortunately, agriculture is moving toward more sustainable practices. However, that doesn't mean that old ways are always better than modern methods.


Be open to old gardening wisdom but keep your thinking cap on. Does that handed-down advice make scientific sense? In the old days, some people believed that beating trees with a stick in the spring would make the sap rise faster and make the trees more productive. Needless to say, that's nonsense.


Next week I'll share some more information on common gardening myths.


Food Growing Forum: Last Sunday of the month through October. Register to get Zoom link at
Sunday, October 25, 3 pm to 4 pm, “Planting Onions, Leeks and Other Alliums and What Else to Do Now”


Napa Library Talks: First Thursday of each month. Register to get Zoom link.


Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email. For more information visit or find us on Facebook or Instagram, UC Master Gardeners of Napa County.