Na dai (Mang cau dai) sugar apple variety is well-known for its awesome taste and good chewy texture. However, one reason why growers would choose other Annona varieties over the Na dai is often because others have more pulp and much less seeds.
In some fruiting cases, in just about three Na dai sugar apples, there may be over 300 seeds?! Something which could possibly be a reason why this sugar apple variety is sold at very expensive prices in grocery stores, sometimes as high as $10/lb in places.
From seed to full fruiting tree, it could take Na dai about 2 years. There are a few simple tips to help the tree grow faster and with big, sweet fruits. And hopefully, with more pulp and a lot less seeds.
Let's find out.
Starting from Seeds
A grower noticed that as a young seedling, if we let the sugar apple grow in a very wide and big pot (especially in the first one or two years), the tree would more likely focus on growing its roots. And thus, not very much of its 'upper body' part or the leaves, stem and branches.
So something we could do when starting the sugar apple or growing it as seedling is to provide some kind of smaller or not way too big pots for them. This is in a way like squeezing them into a smaller house (training with less resources and space). As such, people have seen the young seedlings shoot up fast and grow out leaves.
It could possibly be that old gardening adage "the first year they sleep, the second year they creep, the third year they leap". So it's like, root formation, then branch / leaves formation then shoot up the sky (energy for flowers / fruits). Possibly the smaller pot at an early stage could make the plant 'wake up' sooner?!
When you do the repotting of the plant to a bigger pot, you could consider roughing up the roots a bit. It simply means pulling some pot-bound roots out. Some people are scared that doing so might damage the roots. However, it can help the roots break out of their root-bound circling 'memory' and expand out more in the new house.
Plus, these roots are not very fragile thing so they'll be able to stand and fight for their own. As a note, try to use new soil when you do the repotting. You can use any potting mix that allows the roots to aerate.
It seems that young sugar apple roots react quite well to bone meal. You could mix water into peat moss as the breeding ground for the seeds. And then mix in some bone meal. You can keep the seeds in a container with a lid slightly on to retain the moisture.
Sow the seeds pointed end down as that end is usually where the roots will sprout out first. It just helps it develop a little bit faster. Some young seedlings might have the seed outer shell dangling on (have not opened fully and dropped). It's okay and not really an issue.
The best time to grow the sugar apple is often in the spring season. Because it allows for good root formation. If your sugar apple tree has grown up quite a bit but only has one main stem (no branches), you can consider pruning it in February a subsequent year. For maintenance, this is also a good time to remove old leaves on the tree.
As It's Growing Up
As your sugar apple plant is growing up, remember to introduce it to more sunlight for some 8 hours a day. This could help very much in good fruit production. And also as the tree is getting more light, it will prevent scales or other insects from infecting it as they don't have a humid shady place to live on.
For the first month in the bigger pot, if there's bone meal mixed in with the soil, you may not need to fertilize the soil much any more. As a lot of fertilizer could burn the plant and cause exhaustion.
When the plant grows a little bit bigger, you can lightly fertilize it every 3 months or so. Or sequence feeding it every two weeks or so. Some people do a fish emulsion spray, then two weeks later a milk fertilizer spray. These feeds are light but they help the tree catch up growth fast.
After the liquid fertilizer feed, about 1-2 months after, you can apply other synthesized or chemical fertilizer as you'd like. Some people use Osmocote 14-14-14 or Osmocote Indoor Outdoor.
In the first 2-3 months in the new bigger pot, if we feed the plant chemical fertilizer straight away, it might get easily exhausted, especially in the hot summer season.
After some time that the plant has stabilized, we can feed it more of the chemical fertilizer, for example in the fall, for better growth. Do observe the plant or the weather to feed it a just good enough amount.
The Na dai variety specifically do like cow manure a lot. So you could mix in some or sprinkle it on the top soil. Make sure though not to mix in too much as cow manure can hold quite a bit of moisture and could cause root rot.
To make the fruits sweeter, growers also throw in some Epsom salt every 2 months or so into the soil. Although I haven't tried this one personally, some advice that we don't water the plant in the summer, it will increase the fruit yield. Do have an experiment and if possible we'll let you know how it goes.
Seaweed and potash are said to be very good for the plant, especially in terms of frost protection (although the Na dai variety has quite some good tolerance to the cold compared to some of its other cousins like soursop). If your place has frost in the winter, you can consider spraying the seaweed and potash on your sugar apple plants in the summer to help protect it from the cold and frost.
It is said that these increase the osmotic potential or so in the plants and thus allowing it to hold more water and eventually surviving through the winter. Potash can also help the tree stand strong on its own.
As a cheap or often free fertilizer, you can also use compost. Or those made from vegetable and fruit scraps from your kitchen. When the scraps are still quite fresh, be careful not to put it into the soil with your plant yet. Because it will cause heating as the scraps have not been composted yet (or have not been through the 'heat' phase so the microbial activity on them is still very high). This could cause nutrient competition and stunting the growth of your sugar apple.
To make the compost, you can bury the scraps into a bucket. Within about 2 months, you will have good soil ready to use. Another case where people might put a bucket of veggie scraps under a tree like atemoya (a cousin of sugar apples) is when they want to attract the bugs and beetles to come. Those guys help do the job of pollinating the Annona flowers in the natural environment.
Flowering & Fruiting
Sugar apple plants often bloom in March. People usually do the hand pollination in May or so. You could expect fruits in August or September. It's usually one or two crops a year. Although I heard that you can get two crops a year with some pruning.
Although sugar apple is a naturally productive tree, as one can hold about 100 fruits or more, people often hand pollinate the flowers to improve the shape of the fruit and their size, i.e., bigger more round fruits.
To help a part in making sugar apples with more pulp and less seeds, a simple tip you could try is to reduce the bearing amount of fruits on one plant, especially in the first one or two years.
Some growers, understandably, wanted a lot more fruits so they hand pollinated a lot of flowers and let them grow. It might just be counter-productive as some fruits turned out to have such little flesh and quite frankly a bunch of seeds.
A good amount for its first few years is about 20-30 fruits per plant. You could pollinate a lot of flowers to see. If some fruits set, when they're about the size of a pinkie head, you can have a look. For those that look okay or good, we can keep them and let them grow. For others that may not be looking very strong, we may deliberately pluck them off.
When we have a good amount of fruits on the tree, but flowers are still blooming, you may also consider plucking off some blooms. This is so the tree may focus more of its energy on nourishing the fruits.
Hand pollination can also help with the fruit size. Just as well, pruning off some lateral branches (or branches that grow on the sides of the trunk or along the length of any other branches) can also help with bigger fruits.
When you do the hand pollination, you may just slide the brush with the pollen on gently in one time and then pull out. Try to simulate the touch or movement of an insect just as much as possible.
Learning from the pollinating of other Annona trees like cherimoya, where if you dip in too much pollen or quite a few times into the stigma of the flower, the fruit may just have a lot of seeds. So this is something you may want to try on your sugar apple tree.
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