Why are my geraniums dying?

Question: We have had beautiful geraniums on our back deck for over 30 years. But the last two summers have been a disaster! For the first time last summer we bought our geraniums from Walmart and they soon withered and died. So this year we bought them from an expensive florist and put new dirt in the pots. They all started withering in a few days. We are desperate to have our beloved geraniums back. We would appreciate any suggestions you might have  for what is happening and how to fix the problem.
Thank you so much

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 17, 2023, 4:14 PM EDT
response: One die-off event might have been related to original plant quality (perhaps roots were stressed or dying from being over- or under-watered prior to purchase) but a second failure suggests something else is going on. You mention using new potting soil...was this just to replace some of the prior soil or all of it? (Sometimes pathogens can remain in soil that is re-used for years, plus the soil breaks down over time and becomes more moisture-retentive and more poorly-drained, which is a condition zonal geraniums do not tolerate well.)  Are the containers drained well, with their drain holes remaining unobstructed? Are the containers being checked for watering needs before being watered so the plants aren't staying too wet? We realize that with decades of successful geranium cultivation you likely are well aware of their needs, but we ask to try to narrow-down a potential diagnosis. The coloration of the foliage suggests stress, and root stress in particular as related to soil moisture is one of the most common sources of decline if a pest or disease is not responsible. There is a lesion on the close-up leaf photo (possibly Botrytis) but not of a disease that would be expected to cause this much failure to thrive by itself.  Have the current batch of geraniums been fertilized since they were planted? They look nutrient-starved, though sometimes this is a function of root decline or soil acidity (pH) being outside a plant's preferred range rather than a lack of certain nutrients itself. Frustratingly, some toxicities from an overabundance of certain nutrients can look very similar to those of deficiencies.  In years past was there a source of partial shade over the planters that is now gone? (Either the containers were moved to a sunnier spot, or maybe a tree was pruned, fell, or was removed?) High heat can stress geraniums and cause a leaf "bleaching" type of symptoms, and different cultivars have different levels of sensitivity to temperature.  Once we have a little more information we can also consult with our plant pathologist to see if he recognizes these symptoms, though it may be a few days before we can get his feedback as he is currently unavailable at a horticulture conference.  Miri

responder: The Question Asker Replied July 19, 2023, 9:58 AM EDT
response: Thank you for your thorough response to my question. I appreciate your good suggestions.We did completely change the potting soil in all the containers. (we thought the new soil would contain the necessary nutrients, so we didn’t add fertilizer).We’re not sure about the watering, although we are pretty much watering like we always did. We’re checking the drainage. Until a couple of years ago we were putting stones at the bottom of the pots, because we thought that might help with drainage. We stopped doing that.It’s interesting that you mentioned three shade.  Two years ago we did cut down a tree that provided partial shade to the geraniums. Since we had 50 geraniums around the perimeter of our deck, some of them did not get that shade. But they are all now in full sun.Again, thank you for giving such attention to my question. I hope the information I provided is useful. I could take more photos if that would help.GretchenOn Mon, Jul 17, 2023 at 4:15 PM Ask Extension <<personal data hidden>> wrote:

responder: The Question Asker Replied July 20, 2023, 10:13 AM EDT
response: One thing I forgot to mention, is that a while after we planted the geraniums, almost all the leaves turned red. I am not sure if that is relevant to the problem.On Mon, Jul 17, 2023 at 4:15 PM Ask Extension <<personal data hidden>> wrote:

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 21, 2023, 11:41 AM EDT
response: Hello Gretchen,  Potting soils tend to not contain fertilizer, though some brands do include it. If nutrients were added to the mix it will be mentioned somewhere on the bag label, like a N-P-K formulation listed on fertilizer packages. For now, you can try applying a dose or two (as per product label directions) of liquid fertilizer to see if the youngest foliage on the geraniums gradually greens-up. (We're suggesting something liquid over granular/pelletized because the latter will take longer to start working.) Even if it works well, an improvement in color on the older leaves might not occur as certain nutrients can only move into new growth as opposed to existing/older growth after the plant absorbs them. Nitrogen [N] might be the key nutrient that is deficient in this situation but other candidates include iron [Fe], manganese [Mn], or magnesium [Mg]. All of those can contribute to a greener, evenly-colored leaf, though only trace amounts of the latter three are needed by plants so a drastic supplementation of them is not required beyond what will be included in the fertilizer by itself. Any general-purpose balanced fertilizer that has micronutrients (those beyond just the N-P-K basics, such as Fe, Mn, and Mg) will likely have all of these in the formulation. Any prominent improvement in leaf color as a result of nutrient absorption might take at least a week or two to become apparent.  Zonal geraniums are very tolerant of drying out compared to many annuals, though would prefer to not get too dry between waterings. (They are less tolerant of the opposite -- staying damp.) Feeling the soil about an inch or two deep can help assess soil moisture: if damp to the touch at that depth, watering can probably wait; if somewhat dry at that depth instead, then watering may be needed. Deeper/larger containers can be checked at a greater depth (say, two inches or slightly more) than shallower containers. (So the trough-style planters might be monitored closer to an inch or so deep and the hanging baskets deeper.)  Undrained pots should have holes drilled into their base, if possible, before they are planted. Using stones in a pot with drainage actually tends to worsen drainage, but might sometimes be necessary in pots with no drain holes since there is nowhere for any excess water to go otherwise (though this is not the ideal solution as it risks saturating the root zone if the water table gets too high).  We're not certain if sun exposure intensity was a contributing factor, but it was under consideration since heat tolerance can vary a bit between geranium varieties. In either case, our plant pathologist agrees that Botrytis might be responsible for the brown leaf lesion (quite common on a variety of flowering plants in wet or humid conditions) but it's not a major contributor to the other issues of poor growth and red-veined leaves. Leaf reddening can be a sign of stress, but might have been due to nutrient or acidity (pH) changes, root decline from soil wetness or drying or high heat, or other environmental factors...unfortunately it's hard to determine what exact issue was responsible.  For now, just try to monitor their watering needs and see if a liquid fertilizer has any impact over the next two weeks or so.  Miri

responder: The Question Asker Replied July 22, 2023, 9:09 AM EDT
response: Thanks so much for your very useful advice. We are going to more carefully monitor the watering and try the liquid fertilizer.We really appreciate UMD Extension. Thank you for providing such a valuable service.On Fri, Jul 21, 2023 at 11:41 AM Ask Extension <<personal data hidden>> wrote:

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 24, 2023, 4:20 PM EDT
response: You're welcome!