It's nitrogen deficiency, probably exacerbated by nitrogen "tie-up" from undecomposed wood in the mulch. Fish emulsion fertilizer will solve it if you want to stay organic. All purpose miracle-gro will produce quick results if you're okay with synthetics. I'd supplement that with foliar feeding from either source as often as you can until the problem is abated. Use a more dilute solution for foliar feeding. Squash are very heavy feeders, especially when young. The only explanation I can give for peppers and tomatoes is that peppers grow more slowly to start out with. Tomatoes are also heavy feeders, so I'm not sure why you're not seeing problems there. If they are transplants you bought, it's likely that they were already heavily loaded with fertilizer when you bought them, and that's carrying them over for now. I'm not familiar with soils in California, but it may be prudent to add a source of magnesium and/or calcium to your raised bed soil. Dolomitic lime provides both, but can raise the pH. Lime was probably mixed into the soil you bought, but not the compost. Gypsum is pH neutral and provides calcium. Epsom salts provide magnesium, but are very soluble and therefore must be included in irrigation water. All-purpose miracle grow doesn't contain calcium or magnesium (few fertilizers do because of formulation issues).

Hi Gardenerenthusiast, I am glad you asked this question because the same thing has been happening to me, on both my zucchinis and my spaghetti squashes. Along with rotting blossoms that don't open, I've been getting female blossoms where the squash has shrivelled up before the flower even opens. My plants are otherwise healthy, though I have just started to see some yellowing on the leaves. Unfortunately I have no idea what is causing this, though I've narrowed it down to blossom end rot (which would mean a lack of calcium in the soil) or under watering (it's been very dry here and I've been watering shallowly and regularly, instead of deeply), or some kind of virus/fungus etc. I can't see any trace of pests on my plants, save for a few black aphids, and there are no signs of squash vine borers. One of the strange things is that it suddenly affected my zucchini, spaghetti squashes, and now my delicata squashes all around the same time, even though they are in different garden beds. This makes me think it is either the weather or a virus. My current theory is that I haven't watered them deeply enough, and also that they might need more plant food since they are quite close together and fruiting heavily. Sorry I don't have an answer for you, but I would be curious to know if any of that sounds familiar to you. Good luck!

I concur. You may be burning the plants with such high ppm since the majority of the TDS levels are from NPK. You also will need to add calcium since you took out the main source of calcium, tap water. My suggestion is to half the nutrient strength, and purchase some CalMag supplement and use that to make up for the lack-there-of. If the plants bounce back then you can try to raise the nutrient strength slowly and see how the plants react. Wrinkly leaves usually = Ca deficiency or bugs Burned tips usually = nute burn or light burn This post was edited by ethnobotany on Sat, Jan 12, 13 at 19:57

Fed it what specific liquid fertilizer and how much of it and how old is the plant compared to how may times it has been fed? Feeding a plant 2x in 10 days is not the same thing as feeding the plant 2x in 2 months and the plant is clearly nutrient deficient from the photo And how big is the pot? Zucchini needs a big pot. And how often does it get watered? And what does the entire plant look like? Dave