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

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

You're welcome!