Actually Tulip trees have perfect flowers, meaning they can self pollinate having both male and female parts in the same flower. For Tulip Trees, heavy seed crops tend to compensate for low seed viability (around 5-20 percent). The samaras are wind dispersed to distances 4 and 5 times the height of the parent tree. Seeds require a cold stratification period, and germination rates vary with time and temperature. Under controlled conditions, stratification in moist sand within a temperature range of 32° to 50° F for periods of 70 to 90 days resulted in satisfactory germination. However, seedling yield increases with increasing time of stratification. Generally as temperature decreases and time increases the germination rate increases; for example, 90 percent germination occurred after 140 days at 36 degrees Fahrenheit. Germination is epigeal and occurs when seeds remain constantly moist for several weeks. Seed Germination and seedling development is enhanced on mineral soil or on well-decomposed humus than on a thick, undecomposed litter layer. Germinating yellow-poplar seedlings need a suitable seedbed and adequate moisture to survive and become established. After germination, several critical years follow. During this period sufficient soil moisture must be available, good drainage and protection against drying and frost heaving are necessary, and there must be no severe competition from nearby sprout growth. In a study in which various mulches were used to induce soil temperature variation, seedlings grew faster in warm soil than in cool soil. Soil temperatures as high as 97° F had a beneficial effect on seedling growth.

Yellow variegated leaves in summer or yellow fall color? The typical plant produces nice yellow fall color, but there are also yellow variegated forms being grown. These last will not be as easy to find as non-selected seedlings. Here is a link that might be useful: Monrovia Plant Catalog Search - Liriodendron

Harriet, Is it a new tree that just was planted this year? If so, I would not necessarily be surprised if leaves fell early in its first year in the ground. That would just be a bit of a delayed reaction to being transplanted. There's other reasons for early leaf drop, and they can range from two little moisture to far too much. I'm not sure what your rainfall has been like for the last couple of months, but if it has been skimpy, they might be dropping leaves because of a lack of moisture. During the last 60 days, we have had 1.4" of rain, and 1.2" of that has fallen in the last two weeks, and all my fruit trees suffered horribly during that time. All my peach and plum trees had leaves turning yellow and dropping during that last two months, and it was a combination of drought stress and heat. They could have withstood the heat better if more rain had fallen. Eventually I watered them quite a bit over a period of a few days (they are in the narrow band of sandy-silty soil that cuts across our property and it drains like a sieve) and the leaf yellowing and leaf drop stopped. However, there's also been some years when we had exceptionally heavy rainfall in late summer or early autumn and it has caused the fruit trees to abruptly drop all their leaves earlier than usual. I've never been sure if they did that because of the excess moisture itself or if the moisture and higher RH values caused some sort of fungal leaf infection (there was some spotting on the leaves after the heavy moisture) that caused the leaves to fall. Either way, sometimes the trees turned right around and immediately put out new foliage, and some years they didn't. Regardless, they leafed out, flowered and fruited normally the following spring. The other possibility, depending on what sort of weather you had in your location the past few months, is that the trees had a great spring/early summer and put on tons of new growth because of all the rain. Then, the rain stopped. When that happened so abruptly, the trees were left with more foliage and fruit than they could support under the then-hot late summer weather. This is what happened with my pecans and oaks. They grew like maniacs from all the rain that fell from mid-June 2014-early July 2015. I mean they grew several feet in height during that time when a little over 70" of rain fell. Along with all that new growth there was a great amount of new foliage and lots and lots of nuts. Unfortunately, the rain stopped abruptly and we went into a flash drought within just a few weeks. Right now we are in Severe Drought. How did the nut-bearing trees react? They started dropping leaves and nuts like crazy. The rain stopped in early July. The trees were dropping a tremendous amount of leaves and nuts by early August, and that really hasn't stopped. Just yesterday I noticed tons of acorns on the ground beneath a bur oak that had seemed untouched by the drought, whereas the red oaks and post oaks have been struggling. The bur oak's acorns aren't even half their usual size. I am sure my trees did this because a year of prolonged heavy moisture spurred an unreasonable amount of growth that the trees then could not sustain in hot, dry weather. I'm not worried about the long-term health of the trees here. I think they will be fine. They're just doing what they need to do to survive the drought. Your pear tree likely is reacting to either too little or too much moisture in the same way. Are all the pears dropping or only a portion of them? I don't grow pears so am not familiar with how they fruit, but some fruit trees put on huge loads of fruit and then cannot carry all of that heavy load to maturity. In peach trees, even when you thin the fruit properly while it is very young and small, you still can get a massive amount of fruit drop in late May or early June. It is commonly referred to as June drop and is just the tree acknowledging it is carrying more fruit than it can mature. After the excess fruit drops, the fruit left on the tree goes on and matures just fine. So, if pears abort their own excess fruit like peaches do, that might be what you're seeing with the fruit. My peaches often drop their excess fruit when they are only about 4 or 5 ways from ripening, and that can be very frustrating but it is a natural process of the tree and I can't do anything to prevent it. I think it is the tree's way of telling me it wishes I had thinned the fruit even more than I did. I do thin a lot, or what seems like a lot to me, and some years remove up to 95-95% of the peaches (in a year when it seems like every single blossom formed a fruit), as I did this year, and still we had the June drop. I don't know if I've come up with an exact answer for you, but I think I've given you a couple of possible causes. It has been such a crazy weather year with some very wet weather and some very dry weather and I think that the trees are just reacting to what they've experienced. How if you're seeing any signs of fungal disease on our pear tree, that's a more serious issue. Dawn

it is september .. its totally normal ... and perhaps.. a bit early due to transplant stresses ... plus whatever ma nature threw at it this summer .... cut watering down next year.. to allow it to get to free range the year after ... water perhaps only in drought ... see link for general discourse on such ... i am NEVER concerned about leaf color change/dropping ..... after 9/1 ... and believe it or not.. its very variable year to year ... cant really see the hole ... ken https://sites.google.com/site/tnarboretum/Home/planting-a-tree-or-shrub