What Went Wrong With my Squash?

Diagnosing plant problems is a very normal and vexing part of gardening, but keeping things simple is usually the best way to figure out what's wrong.

My squash grew poorly this year. For a good part of the season the leaves were a light color of green (rather than a nice deep green), and the leaves were not as large as they should have been. It is now mid-September and I expect a poor harvest this fall. There are many possible reasons why this happened, and I thought that sorting through them would be a good way to make a point about diagnosing plant and soil problems.

Lack of color, stunted growth, and a poor yield. Most years I have too many squash - but this year I might only get a few meals out of them!

From the questions, answers, and conversations I have seen on the internet, regardless of the plant, most people figure stuff out but running on gut feelings, asking others, or looking to one solution as a panacea for all problems (e.g. Epsom salts). By contrast, I think a better way is to begin by considering the needs of the plant, and then to work back from that by thinking about which of them is most likely to have not have been adequately met, and using the available evidence to arrive at a plausible explanation.

Let’s think of what squash need to grow well. They need lots of sunlight, a collection of minerals and nutrients (N,P,K, etc.), constant moisture, warm soil, and soil acidity ranging from a pH of 6.0 to 7.0.

Sunlight

People often overlook a lack of sunlight as a potential cause for poor plant performance. All plants need sunlight to grow, develop and stay healthy, and it is very important for heat loving plants. Thankfully, my squash were planted in the middle of the garden in full sun, with nothing to cast shade on them at any part of the day. There is no chance that they did not get enough sun.

Minerals and Nutrients

Squash are notorious “heavy feeders”. They need a lot of everything to grow well. To be specific, they need Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S), Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), and Boron (B), and all in the right amounts. A lack in the right amount of any of these will negatively affect plant health. The problem is that in the absence of a soil test, it can be hard to know which one is actually missing, because many plant problems can have multiple causes. It is also the case that there are other things that can affect a plant’s ability to take up nutrients from the soil - so while it can appear that a plant is not getting enough N or P or K - there may be PLENTY of those things in the soil, but the plant just can’t get them for one reason or another.

My squash look like they need nitrogen. The leaves are not as green as they should be, and the growth rate has been slow. It may be the case that more nitrogen at various intervals throughout the summer may have helped them - but for the reasons stated above, there may have been other factors at play.